Prepreg laminates, composite structures, and methods for manufacturing composite structures

Abstract

The purpose of the present invention is to obtain a prepreg laminate that is a fiber-reinforced plastic material having high rigidity and low weight and moreover having exceptional properties for molding into complicated shapes.　The present invention is a prepreg laminate obtained by a prepreg (A), in which non-continuous reinforcing fibers are impregnated with a thermosetting resin or a thermoplastic resin, and a prepreg (B), in which non-continuous reinforcing fibers are impregnated with a thermoplastic resin, being adjacently laminated, and by the prepreg (A) being disposed on at least one surface, at least some combinations of the adjacent prepregs (A) and (B) forming an overlap region that satisfies (1) and / or (2) below. (1) The coefficient of variation in the fiber length of the non-continuous reinforcing fibers included in the prepreg (B) is greater than the coefficient of variation in the fiber length of the non-continuous reinforcing fibers included in the prepreg (A). (2) The prepreg (B) has a plurality of notches at which the non-continuous reinforcing fibers included in the prepreg (B) are cut, and the average value of a two-dimensional orientation angle of the non-continuous reinforcing fibers included in the prepreg (B) is greater than the average value of a two-dimensional orientation angle of the non-continuous reinforcing fibers included in the prepreg (A).

Description

[Technical Field]

[0001] The present invention relates to a prepreg laminate comprising a prepreg (A) in which discontinuous reinforcing fibers are impregnated with a thermosetting resin or a thermoplastic resin, and a prepreg (B) in which discontinuous reinforcing fibers are impregnated with a thermoplastic resin, and to a composite structure obtained from the laminate. [Background technology]

[0002] Fiber-reinforced plastics, composed of reinforcing fibers and matrix resin, are lightweight and highly rigid, making them widely used in electrical and electronic applications, civil engineering and construction, automotive, sports, and aerospace applications. In recent years, there has been a growing market demand for fiber-reinforced plastics with complex shapes, particularly in the automotive, aerospace, and sports product sectors.

[0003] As a technology to improve conformability to complex shapes, for example, a so-called prepreg has been developed in which a prepreg made by impregnating resin with continuous reinforcing fibers aligned in one direction is given notches to divide the reinforcing fibers (Patent Document 1). In addition, as a technology to improve lightness, for example, a fiber-reinforced plastic has been developed that is composed of discontinuous reinforcing fibers and thermoplastic resin and contains voids (Patent Document 2).

[0004] While fiber-reinforced plastics containing voids, as described in Patent Document 2, offer excellent lightweight properties, a certain degree of reduced rigidity is unavoidable. Patent Document 2 attempts to achieve both lightweight properties and rigidity by creating a sandwich structure in which a fiber-reinforced plastic with voids is used as the core material, and a fiber-reinforced plastic using continuous reinforcing fibers is used as the skin material.

[0005] However, the sandwich structure described in Patent Document 2 had poor conformability to complex shapes because the skin material contained continuous reinforcing fibers. Therefore, Patent Document 3 describes an invention that improves shape-forming ability while minimizing the reduction in rigidity by using discontinuous reinforcing fibers in a sandwich structure in which the core material is a fiber-reinforced plastic having discontinuous reinforcing fibers, resin, and voids. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 5223354 [Patent Document 2] International Publication No. 2015 / 029634 [Patent Document 3] International Publication No. 2018 / 117181 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, in the invention described in Patent Document 3, the discontinuous reinforcing fibers of the core layer tend to interfere with each other during deformation when forming complex shapes, resulting in poor shape conformability of the core material to the skin material. In particular, forming shapes with varying thicknesses is difficult, and there are still limitations on the shapes that can be formed.

[0008] The present invention has been made in view of the above problems, and its objective is to obtain a prepreg laminate, which is a fiber-reinforced plastic material that has high rigidity and lightness, as well as excellent moldability into complex shapes. [Means for solving the problem]

[0009] One aspect of the present invention for solving the above problems is a prepreg laminate in which a prepreg (A) in which discontinuous reinforcing fibers are impregnated with a thermosetting resin or a thermoplastic resin and a prepreg (B) in which discontinuous reinforcing fibers are impregnated with a thermoplastic resin are laminated adjacent to each other, and the prepreg (A) is disposed on at least one surface, and at least a part of the combination of the adjacent prepregs (A) and prepreg (B) satisfies at least one of the following (1) and (2). Suju Complex region area Formation The discontinuous reinforcing fibers contained in prepreg (B) are in a web form, prepreg (A) has a plurality of cuts, and the discontinuous reinforcing fibers contained in prepreg (A) are formed by cutting continuous reinforcing fibers arranged in one direction through the cuts, forming fiber bundles arranged in one direction, prepreg (B) has a plurality of cuts that cut at least a portion of the web-form discontinuous reinforcing fibers, and the cut region in prepreg (A) where the cuts are formed and the cut region in prepreg (B) where the cuts are formed overlap to form the overlapping region, and in the overlapping region, the prepreg (A) and prepreg (B) have 1m , , [Figure 2] , [Figure 1] The sum of the cut lengths converted to per unit area is Ca[m / m 2 ], Cb[m / m 2 When ] is set, the following conditions must be met: It is a prepreg laminate. (1) The coefficient of variation of the fiber length of the discontinuous reinforcing fibers contained in the prepreg (B) is larger than the coefficient of variation of the fiber length of the discontinuous reinforcing fibers contained in the prepreg (A). (2) The prepreg (B) has a plurality of cuts for cutting the discontinuous reinforcing fibers contained in the prepreg (B), and the average value of the two-dimensional orientation angle of the discontinuous reinforcing fibers contained in the prepreg (B) is larger than the average value of the two-dimensional orientation angle of the discontinuous reinforcing fibers contained in the prepreg (A).

[0010] Furthermore, a composite structure having a layer structure formed by molding the prepreg laminate of the present invention is also grasped as one aspect of the present invention.

Effect of the Invention

[0011] According to the present invention, it is possible to obtain a composite structure that has high followability to complex shapes and achieves both high mechanical properties and light weight.

Brief Description of the Drawings

[0012] [Figure 1] It is a schematic diagram showing an example of the prepreg (A) or prepreg (B) of the present invention. [Figure 2] It is a schematic diagram showing an example of the cut arrangement of the prepreg (A) or prepreg (B) of the present invention. [Figure 3] This is a schematic diagram showing an example of the orientation of the reinforcing fibers in the prepreg (B) of the present invention. [Figure 4] This is a schematic diagram showing an example of an embodiment of the present invention. [Figure 5] This is a schematic diagram showing an example of an embodiment of the present invention. [Modes for carrying out the invention]

[0013] <Prepreg (B)> The prepreg (B) in the present invention is made by impregnating discontinuous reinforcing fibers with a thermoplastic resin.

[0014] There are no particular restrictions on the reinforcing fibers used as discontinuous reinforcing fibers (hereinafter sometimes simply referred to as "reinforcing fibers") in the prepreg (B). For example, carbon fibers, glass fibers, aramid fibers, alumina fibers, silicon carbide fibers, boron fibers, metal fibers, natural fibers, mineral fibers, etc., can be used, and two or more of these may be used in combination. Among these, carbon fibers such as PAN-based, pitch-based, and rayon-based fibers are preferably used because they have high specific strength, specific stiffness, and excellent weight reduction effects. Furthermore, from the viewpoint of improving the economic efficiency of the resulting molded product, glass fibers can be preferably used. From the viewpoint of balancing mechanical properties and economic efficiency, using carbon fibers and glass fibers in combination is also a preferred embodiment. Furthermore, from the viewpoint of improving the shock absorption and shapeability of the resulting molded product, aramid fibers can be preferably used. From the viewpoint of balancing mechanical properties and shock absorption, using carbon fibers and aramid fibers in combination is also a preferred embodiment. Alternatively, from the viewpoint of improving the conductivity of the resulting molded product, reinforcing fibers coated with metals such as nickel, copper, or ytterbium can also be used.

[0015] In the present invention, the reinforcing fibers contained in the prepreg (B) are discontinuous reinforcing fibers. This configuration provides excellent shape conformability and facilitates the manufacture of composite structures with complex shapes. In this specification, discontinuous reinforcing fibers mean reinforcing fibers with an average fiber length of 100 mm or less.

[0016] Methods for measuring the average fiber length of reinforcing fibers include, for example, directly extracting reinforcing fibers from the discontinuous reinforcing fibers contained in the prepreg (B) and measuring them by microscopic observation, or dissolving the thermoplastic resin in the prepreg (B) using a solvent that dissolves only the thermoplastic resin, filtering out the remaining reinforcing fibers, and measuring them by microscopic observation (dissolution method). If a solvent that dissolves the thermoplastic resin is unavailable, there is also a method of burning off only the thermoplastic resin within a temperature range where the reinforcing fibers do not oxidize and lose weight, separating the reinforcing fibers, and measuring them by microscopic observation (burning method). Using these methods, 100 reinforcing fibers can be randomly selected, their lengths measured to the nearest 1 μm using an optical microscope, and the average value taken as the average fiber length. It should be noted that when comparing the method of directly extracting reinforcing fibers from the discontinuous reinforcing fibers contained in the prepreg (B) with the method of extracting reinforcing fibers from the prepreg (B) using the burning or dissolution method, there is no significant difference in the results obtained by appropriately selecting the conditions. The coefficient of variation (standard deviation / mean × 100) of the fiber length of the reinforcing fibers contained in the prepreg (B) of the present invention is preferably 20% or more, and more preferably 30% or more. With this configuration, the reinforcing fibers contained in the prepreg (B) have various fiber lengths, resulting in an excellent balance between expansion and shape conformability during molding.

[0017] The discontinuous reinforcing fibers contained in the prepreg (B) are preferably in web form, i.e., a discontinuous reinforcing fiber web. The reinforcing fibers contained in such a discontinuous reinforcing fiber web are usually oriented in three or more directions within the plane. By using a discontinuous reinforcing fiber web, it becomes easy to randomly disperse the reinforcing fibers in the prepreg (B), and as a result, a prepreg with isotropic mechanical properties and moldability can be obtained. As the discontinuous reinforcing fiber web, a nonwoven fabric obtained by a dry or wet method is preferred.

[0018] Such discontinuous reinforced fiber webs may have the reinforcing fibers sealed with other components such as a binder resin. The binder resin is preferably selected from either a thermoplastic resin or a thermosetting resin, from the viewpoint of adhesion between the resin and the reinforcing fibers and sealing only the reinforcing fibers to ensure handling. From the viewpoint of adhesion between the resin and the reinforcing fibers, a resin of the same type as or compatible with the thermoplastic resin to be impregnated, as described later, is selected, and from the viewpoint of ensuring the handling of the reinforcing fibers, an aqueous solution, dispersion, or emulsion of a thermosetting resin or thermoplastic resin is preferred.

[0019] The thermoplastic resin used to impregnate the discontinuous reinforcing fibers in the prepreg (B) is not particularly limited, but examples include polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), and liquid crystal polyester; polyolefins such as polyethylene (PE), polypropylene (PP), and polybutylene; polyarylene sulfides such as polyoxymethylene (POM), polyamide (PA), and polyphenylene sulfide (PPS); polyketone (PK), polyetherketone (PEK), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyethernitrile (PEN), and polytetrafluoroethylene. Examples of thermoplastic resins include fluoropolymers such as styrene, crystalline resins such as liquid crystal polymer (LCP), amorphous resins such as styrene, polycarbonate (PC), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), polyphenylene ether (PPE), polyimide (PI), polyamide-imide (PAI), polyetherimide (PEI), polysulfone (PSU), polyethersulfone, and polyarylate (PAR), as well as phenolic resins, phenoxy resins, and thermoplastic elastomers such as polystyrene, polyolefin, polyurethane, polyester, polyamide, polybutadiene, polyisoprene, fluoropolymers, and acrylonitrile, as well as copolymers and modified versions thereof. In particular, polyolefins are preferred from the viewpoint of lightweight properties of the resulting molded product; polyamides from the viewpoint of strength; amorphous resins such as polycarbonate and styrene-based resins from the viewpoint of surface quality; polyarylene sulfide from the viewpoint of heat resistance; polyetheretherketone from the viewpoint of continuous use temperature; and fluororesins from the viewpoint of chemical resistance.

[0020] As the thermoplastic resin, a blended resin containing multiple types of the above-mentioned thermoplastic resins may be used, and a blended resin mixed with a thermosetting resin may be used as long as the main component of the above-mentioned thermoplastic resin matrix (a component exceeding 50% by weight when the entire matrix is ​​considered to be 100% by weight) is a thermoplastic resin. In other words, "thermoplastic resin" in this specification means a resin composition that contains more than 50% by weight of a thermoplastic resin and exhibits the behavior of a thermoplastic resin as a whole.

[0021] The prepreg (B) of the present invention preferably includes a discontinuous reinforced fiber web and has a plurality of notches that cut at least a portion of the discontinuous reinforced fibers constituting the discontinuous reinforced fiber web. By having such notches, the fiber length of some of the reinforced fibers is further shortened, and the ends of the cut reinforced fibers are arranged in a straight or curved shape, so that the notches open without the reinforced fibers becoming taut when forming complex shapes. In addition, the transmission of interference between the reinforced fibers is interrupted by the division of the reinforced fibers by the notches, making it easier to conform to complex shapes.

[0022] The present invention will be described below with reference to the drawings as appropriate to facilitate understanding, but the present invention is not limited in any way by these drawings. Furthermore, the description of specific embodiments shown in the drawings can also be understood as a description of prepreg (B) as a higher-level concept. In addition, as will be described later, the description of the cut form of prepreg (B) can also be applied mutatis mutandis to prepreg (A) in the present invention.

[0023] In the embodiment shown in Figure 1, the prepreg (B) 3 has notches 1 that cut at least a portion of the discontinuous reinforcing fibers. The notches may be provided over the entire surface of the prepreg (B) or only on a portion of it. They may also be provided on both sides or on only one side. In this specification, the area on the surface of the prepreg (B) in which the notches are provided will be referred to as the "notched area". As shown in Figure 1, the boundary of the notched area 2 is demarcated by a group of line segments formed by connecting the ends of the outermost notches in the area. Such a group of line segments is drawn such that all notches are included within the group and the sum of the lengths of the group of line segments is minimized. That is, the prepreg (B) of the present invention may have a notched area covering the entire surface or a notched area provided on only a portion of the surface.

[0024] The shape of the cut is not particularly limited; it may be a straight line, a shape with a bent section, or a shape with a curved section in part or all of it. However, in order to stably create a cut, it is preferable that the cut be a straight line.

[0025] The length of the cut is not particularly limited, but it is preferably 0.1 mm or more, and more preferably 0.5 mm or more, in order to facilitate the opening of the cut during molding. On the other hand, in order for the prepreg (B) of the present invention to have sufficient mechanical properties when molded into a composite structure, the length of the cut is preferably 50 mm or less, and more preferably 10 mm or less. The length of the cut refers to the length along the cut from one end to the other end of the cut in question.

[0026] In the cut-in region, it is preferable that the cuts are formed with a constant pattern in a plan view. In such a form, it is possible to exhibit homogeneous shape followability and suppress large-scale breaks caused by the connection of the cuts during molding. Note that the cuts being formed with a constant pattern in a plan view means, as described using FIG. 2, that when more than 90% of the area of the cut-in region 2 of the prepreg (B) is arranged by laying out cut units 4 each consisting of two or more cuts 1.

[0027] The sum of the cut lengths converted per 1 m 2 in the cut-in region is preferably 40 m or more. In such a form, the shape followability of the prepreg (B) is greatly improved. More preferably, the sum of the cut lengths 2 converted per 1 m is 100 m or more, and more preferably 200 m or more. There is no particular limitation on the upper limit of the sum of the cut lengths, but in order to prevent the prepreg (B) from being severely broken during molding, it is preferably not more than 1000 m. When converting the sum of the cut lengths, calculate the sum of the cut lengths exposed on the front and back surfaces of the prepreg (B) where the area is at least 0.01 m 2 or more, and convert it to the sum of the cut lengths per 1 m 2 from that value. When the sum of the cut lengths on the front and back surfaces is different, adopt the larger value as the sum of the cut lengths. For example, if the area of the cut-in region 2 on both the front and back surfaces of the prepreg (B) is 0.01 m 2 each, and the sum of the cut lengths on the front surface is 0.5 m and the sum of the cut lengths on the back surface is 1 m, the sum of the cut lengths 2 converted per 1 m is 100 m.

[0028] In prepreg (B), it is preferable that the discontinuous reinforcing fibers are in the form of single fibers. The single-fiber form of the reinforcing fibers allows the prepreg (B) to exhibit more homogeneous shape conformability, resulting in homogeneous mechanical properties upon molding, and suppressing stress concentration at the ends of the reinforcing fibers, thus enabling the development of high mechanical properties. Here, "single-fiber form" refers to a state in the prepreg (B) where the reinforcing fiber singles are not bundled together but independently dispersed. In this invention, when measuring the two-dimensional orientation angle described later for a reinforcing fiber single arbitrarily selected from the prepreg (B) and the reinforcing fiber singles intersecting that single, if the proportion of reinforcing fiber singles with a two-dimensional orientation angle of 1° or more is 80% or more, then it is determined that the discontinuous reinforcing fibers are in the form of single fibers. Here, since it is difficult to identify all the reinforcing fiber singles intersecting the selected reinforcing fiber single, 20 intersecting reinforcing fiber singles are randomly selected and their two-dimensional orientation angles are measured. This measurement is repeated a total of five times with a different reinforced fiber monofilament, and the percentage of monofilaments with a two-dimensional orientation angle of 1° or more is calculated.

[0029] The two-dimensional orientation angle will be explained in detail using Figure 3. Figure 3 is a schematic diagram showing the dispersion state of reinforcing fibers when only the reinforcing fibers are extracted from the prepreg (B) of the present invention and observed from the thickness direction. Focusing on the reinforcing fiber single filament 5a, it intersects with the reinforcing fiber single filaments 5b1 to 5b5. Here, "intersection" means that in the observed two-dimensional plane, the reinforcing fiber single filament of interest is observed to intersect with other reinforcing fiber single filaments, and it is not necessary for the reinforcing fiber single filaments 5a and 5b1 to 5b5 to be in contact in the actual prepreg (B). The two-dimensional orientation angle is defined as the two-dimensional orientation angle 6 between 0° and 90°, which is one of the two angles formed by two intersecting reinforcing fiber single filaments.

[0030] There are no particular restrictions on the method for measuring the average value of the two-dimensional orientation angle from the prepreg (B), but one example is to observe the orientation of the reinforcing fibers from the surface of the prepreg (B). In this case, polishing the surface of the prepreg (B) to expose the fibers makes it easier to observe the reinforcing fibers. Another example is to observe the orientation of the reinforcing fibers using transmitted light on the prepreg (B). In this case, slicing the prepreg (B) thinly makes it easier to observe the reinforcing fibers. Furthermore, another example is to obtain an orientation image of the reinforcing fibers by transmitting light through the prepreg (B) using X-ray CT. In the case of reinforcing fibers with high X-ray transparency, mixing tracer fibers with the reinforcing fibers or applying a tracer agent to the reinforcing fibers makes it easier to observe the reinforcing fibers.

[0031] Furthermore, in the prepreg (B), it is preferable that the discontinuous reinforcing fibers are randomly oriented in the plane. This configuration allows for isotropic shape conformability and mechanical properties. Random orientation of reinforcing fibers in the plane means that the average value of the two-dimensional orientation angle of the reinforcing fibers is within the range of 30° to 60°. The average value of the two-dimensional orientation angle is more preferably within the range of 40° to 50°, and is preferable as it approaches the ideal angle of 45°. The average value of the two-dimensional orientation angle in this invention is measured by calculating the average value of the two-dimensional orientation angles of all reinforcing fiber single filaments (reinforcing fiber single filaments 5b1 to 5b5 in Figure 3) that intersect a randomly selected reinforcing fiber single filament (reinforcing fiber single filament 5a in Figure 3). If there are many reinforcing fiber single filaments intersecting reinforcing fiber single filament 5a, 20 intersecting reinforcing fiber single filaments may be randomly selected and measured. If there are no intersecting reinforcing fiber single filaments with respect to reinforcing fiber single filament 5a, the two-dimensional orientation angle is set to 0°. Furthermore, if there are fewer than 20 reinforcing fiber single filaments intersecting a reinforcing fiber single filament 5a, the number of reinforcing fiber single filaments for which the two-dimensional orientation angle is measured may be less than 20, and the two-dimensional orientation angle shall be measured only for the reinforcing fiber single filaments in which intersection has been confirmed. This measurement shall be repeated at least 5 times with a different reinforcing fiber single filament, and the average value of the total of 100 two-dimensional orientation angles shall be taken as the average value of the two-dimensional orientation angle. If there are no intersecting reinforcing fiber single filaments with respect to the reinforcing fiber single filament 5a, and the two-dimensional orientation angle is set to 0°, this two-dimensional orientation angle shall be counted as 1.

[0032] <Prepreg (A)> In the present invention, the prepreg (A) is made by impregnating discontinuous reinforcing fibers with a thermosetting resin or a thermoplastic resin.

[0033] The reinforcing fibers included in prepreg (A) can be the same as those used in prepreg (B) described above.

[0034] When the resin used in the prepreg (A) is a thermosetting resin, the thermosetting resin impregnated into the discontinuous reinforcing fibers is not particularly limited, but examples include epoxy resin, unsaturated polyester resin, vinyl ester resin, phenolic resin, epoxy acrylate resin, urethane acrylate resin, phenoxy resin, alkyd resin, urethane resin, maleimide resin, cyanate resin, etc., and epoxy resin is particularly preferred from the viewpoint of mechanical properties. As the thermosetting resin, a blended resin containing multiple types of the above thermosetting resins may be used, and a blended resin mixed with a thermoplastic resin may be used as long as the main component of the thermosetting resin matrix (a component exceeding 50% by weight when the entire matrix is ​​considered to be 100% by weight) is a thermosetting resin. That is, "thermosetting resin" in this specification means a resin composition containing more than 50% by weight of a thermosetting resin and exhibiting the behavior of a thermosetting resin as a whole.

[0035] If the resin used in prepreg (A) is a thermoplastic resin, the same thermoplastic resin as that used in prepreg (B) described above can be used.

[0036] The reinforcing fibers contained in prepreg (A) are discontinuous reinforcing fibers. This configuration provides excellent shape conformability, making it easy to manufacture fiber-reinforced plastics with complex shapes. The same method used to measure the average fiber length of the reinforcing fibers as described above for measuring the fiber length of the discontinuous reinforcing fibers contained in prepreg (B) can be used. The coefficient of variation (standard deviation / mean × 100) (%) of the fiber length of the discontinuous reinforcing fibers contained in prepreg (A) of the present invention is preferably less than 20%, and more preferably less than 10%. This configuration allows for control of the fiber length of the discontinuous reinforcing fibers contained in prepreg (A), making it possible to exhibit stable mechanical properties.

[0037] The prepreg (A) preferably contains fiber bundles made of discontinuous reinforcing fibers. This configuration is preferred because it provides an excellent balance between mechanical properties and shape conformability. Here, the fiber bundle refers to an aggregate of discontinuous reinforcing fibers such that the average value of the two-dimensional orientation angle is 0° or more and less than 30°.

[0038] It is more preferable that the prepreg (A) contains fiber bundles made of discontinuous reinforcing fibers arranged in one direction. By aligning the fiber bundles in one direction, the volume content of reinforcing fibers can be increased, resulting in a prepreg with high mechanical properties. Furthermore, by having discontinuous reinforcing fibers while being arranged in one direction, shape-following ability to complex shapes can be obtained.

[0039] Whether or not fiber bundles are aligned in one direction can be determined as follows. First, a virtual reference line is set on the prepreg, and the fiber orientation angle, defined by the angle between the average fiber orientation direction of each discontinuous reinforcing fiber constituting the fiber bundle and the reference line, is calculated for 100 discontinuous reinforcing fibers contained in the target fiber bundle, and the average value is taken as the orientation angle of the fiber bundle. Here, if the difference between the orientation angle of one fiber bundle and the orientation angle of another fiber bundle is less than 10°, the two fiber bundles are judged to be a pair aligned in the same direction. Then, 20 comparison fiber bundles are randomly selected for any fiber bundle contained in the prepreg, and if all of these comparison fiber bundles are judged to be aligned in the same direction as the aforementioned fiber bundle, the fiber bundles contained in the prepreg are judged to be aligned in one direction.

[0040] In particular, in the portion of prepreg (A) containing discontinuous reinforcing fibers, it is preferable that there be multiple cuts, and that the discontinuous reinforcing fibers contained in prepreg (A) are formed when continuous reinforcing fibers arranged in one direction are cut by these cuts, thereby forming fiber bundles of discontinuous reinforcing fibers arranged in one direction. The length and arrangement of the cuts in this form are the same as those of prepreg (B) described above, so a further explanation is omitted.

[0041] In another form, the discontinuous reinforcing fibers contained in the prepreg (A) may be arranged in five or more directions within the plane. When the difference between the orientation angle of one fiber bundle and the orientation angle of another fiber bundle is 10° or more, the fiber bundles are judged to be a pair arranged in different directions. For any fiber bundle, if there are five or more pairs of fiber bundles arranged in different directions, and the difference in the arrangement direction of each pair is 10° or more, the fiber bundles are judged to be arranged in five or more directions within the plane. The number of arrangement directions of the prepreg (A) in this form is measured by observing the fiber bundles on the surface of the prepreg (A) with a microscope. When the fiber bundles of the prepreg (A) are arranged in five or more directions, it becomes easier for them to flow isotropically, and the shape-following ability for complex shapes is improved. More preferably, when the fiber bundles of the prepreg (A) are arranged in eight or more directions, it becomes even easier for them to flow isotropically. Even more preferably, the fiber bundles are randomly and uniformly arranged. An example of such a substrate form is SMC (Sheet Molding Compound).

[0042] <Prepreg laminate> The prepreg laminate of the present invention is formed by laminating prepreg (B) and prepreg (A) adjacent to each other, with prepreg (A) arranged on at least one surface. The number of layers of prepreg (B) and prepreg (A) is not particularly limited, as long as there is one or more pairs of prepreg (B) and prepreg (A) arranged adjacent to each other. From the viewpoint of mechanical properties, it is more preferable that prepreg (A) is arranged on both surfaces of the prepreg laminate. Furthermore, from the viewpoint of suppressing warping of the resulting molded product, it is preferable that the lamination configuration of prepreg (B) and prepreg (A) is such that they are laminated symmetrically with respect to the center of the lamination direction of the prepreg laminate. An example of such a lamination configuration is a [prepreg (A) / prepreg (A) / prepreg (B) / prepreg (B) / prepreg (A) / prepreg (A)] lamination configuration.

[0043] In a first embodiment of the present invention, in at least some combinations of adjacent prepregs (A) and prepregs (B), a region is formed in which the coefficient of variation of the fiber length of the discontinuous reinforcing fibers contained in prepreg (B) is greater than the coefficient of variation of the fiber length of the reinforcing fibers contained in prepreg (A). Because the variation in the fiber length of the discontinuous reinforcing fibers contained in prepreg (A) in this region is smaller than that of prepreg (B), the mechanical properties are stable and a high reinforcing effect can be obtained. Furthermore, the large variation in the fiber length of the discontinuous reinforcing fibers contained in prepreg (B) means that the longer discontinuous reinforcing fibers contribute to high mechanical properties and expandability, and the shorter discontinuous reinforcing fibers flow under pressure during molding, thus contributing to high shape conformability.

[0044] Furthermore, in a second embodiment of the present invention, in at least some combinations of adjacent prepregs (A) and prepregs (B), prepreg (B) has a plurality of notches that cut the discontinuous reinforcing fibers contained in prepreg (B), and forms a region in which the average value of the two-dimensional orientation angle of the discontinuous reinforcing fibers contained in prepreg (B) is greater than the average value of the two-dimensional orientation angle of the discontinuous reinforcing fibers contained in prepreg (A). In this region, the presence of a plurality of notches in prepreg (B) that cut the discontinuous reinforcing fibers contained in prepreg (B) causes the notches to open during molding, improving shape conformability and making it easier to conform to complex shapes such as thickness changes and uneven shapes. Furthermore, because the average two-dimensional orientation angle of the discontinuous reinforcing fibers contained in prepreg (B) in the region is greater than the average two-dimensional orientation angle of the discontinuous reinforcing fibers contained in prepreg (A), prepreg (B) has isotropic flow properties and therefore exhibits high shape-following ability even when the molded shape is complex, and prepreg (A), which is placed on at least one surface of the prepreg laminate, exhibits high mechanical properties. When prepreg (A) contains the aforementioned fiber bundle, the two-dimensional orientation angle of prepreg (A) shall be measured by selecting from the group of reinforcing fiber monofilaments that form the same fiber bundle. In this specification, the region in which prepreg (A) and prepreg (B) are in contact, as shown in the first or second embodiment above, shall be referred to below as the "overlapping region". Furthermore, in this specification, the portions of prepreg (A) and prepreg (B) that form overlapping regions with adjacent prepreg (B) and prepreg (A), respectively, may be referred to as "overlapping region of prepreg (A)" and "overlapping region of prepreg (B)."

[0045] Thus, in the overlapping region, by ensuring that the coefficient of variation of the fiber length and the two-dimensional orientation angle of the reinforcing fibers contained in prepreg (A) and prepreg (B) satisfy the above relationship, a composite structure with excellent mechanical properties, shape conformability, and lightweight properties can be formed. In this invention, the first and second embodiments are not mutually exclusive, and the invention also encompasses embodiments that satisfy both the first and second embodiments. In the prepreg laminate of the present invention, the entire surface of adjacent prepreg (A) and prepreg (B) may be an overlapping region. It is a preferred embodiment of the present invention that all adjacent prepreg (A) and prepreg (B) have such an overlapping region.

[0046] A more preferred form of the prepreg laminate of the present invention is one in which, in the overlapping region, the average fiber length of the discontinuous reinforcing fibers contained in prepreg (A) is longer than the average fiber length of the discontinuous reinforcing fibers contained in prepreg (B). The relatively longer fiber length of prepreg (A) allows for higher mechanical properties after molding, while the relatively shorter fiber length of prepreg (B) allows for higher shape conformability. This effect is particularly pronounced in a prepreg laminate in which prepreg (B) is laminated between two prepregs (A). Furthermore, in the overlapping region, it is more preferable when, in terms of the number of fibers, 50% or more of the discontinuous reinforcing fibers contained in prepreg (B) have a fiber length less than or equal to the average fiber length of the reinforcing fibers contained in prepreg (A), as this provides an excellent balance between mechanical properties and shape conformability.

[0047] A more preferred embodiment of the prepreg laminate of the present invention is a configuration in which prepreg (A) has a plurality of cuts, and the discontinuous reinforcing fibers contained in prepreg (A) are formed by cutting continuous reinforcing fibers arranged in one direction through these cuts, thereby forming fiber bundles arranged in one direction, and prepreg (B) has a plurality of cuts that cut at least a portion of the web-shaped discontinuous reinforcing fibers, and an overlapping region is formed by the overlap of the cut regions in prepreg (A) and the cut regions in prepreg (B). The overlapping region here is the region formed when the cut regions contained in prepreg (B) and prepreg (A), which are laminated adjacent to each other, are superimposed in the lamination direction, and their respective cut regions overlap. With this configuration, adjacent prepreg (A) and prepreg (B) both conform to the shape in the overlapping region, so that mechanical properties and shape conformability are efficiently expressed.

[0048] Furthermore, in the overlapping region, the 1m of prepreg (A) and prepreg (B) 2 The sum of the cut lengths converted to per unit area is Ca[m / m 2 ], Cb[m / m 2 When this is the case, it is preferable that 0.1 ≤ Cb / Ca < 5 be satisfied. This configuration is preferable because it offers an excellent balance between mechanical properties and shape conformability. Furthermore, it is preferable that 0.2 ≤ Cb / Ca ≤ 4 is preferred from the viewpoint of mechanical properties and shape conformability, and it is even more preferable that 0.5 ≤ Cb / Ca ≤ 2 is preferred. Considering the manufacturing process, setting Cb / Ca = 1 is preferable because it is possible to make the sum of the cut lengths the same and to adopt the same cut pattern for prepreg (A) and prepreg (B).

[0049] In a more preferred embodiment of the prepreg laminate of the present invention, in the aforementioned cut region, the cuts of prepreg (A) and prepreg (B) are formed in a certain pattern as described above in a plan view, and in the overlapping region, when the cut pattern of prepreg (A) and the cut pattern of prepreg (B) are projected in the thickness direction, at least a portion of the cuts of both intersects. With this embodiment, the portion of prepreg (A) that is particularly excellent in shape following and the region of prepreg (B) that contains short, discontinuous reinforcing fibers are in close proximity, so that short fibers can easily flow into the thickness change portion, resulting in excellent thickness change following ability.

[0050] <Method for manufacturing composite structures> A method for manufacturing a composite structure of the present invention using the prepreg laminate of the present invention includes heating and pressurizing a preform containing the prepreg laminate of the present invention. Here, the preform refers to a molded substrate containing at least a portion of the prepreg laminate of the present invention, and may contain materials other than the prepreg laminate of the present invention. Examples of materials other than the prepreg laminate of the present invention include, from the viewpoint of improving mechanical properties, fiber-reinforced plastic precursors such as unidirectional continuous fiber prepregs and woven fabric prepregs; from the viewpoint of improving mechanical properties and appearance, metal layers such as metal foils and metal plates; and from the viewpoint of improving moldability, resin layers that do not contain reinforcing fibers. However, the method is not limited to these, and any material can be used.

[0051] A more preferred embodiment of the method for manufacturing the composite structure of the present invention using the prepreg laminate of the present invention comprises a heating and pressurizing step of heating and pressurizing the prepreg (B) to a temperature at which the thermoplastic resin melts or softens, and an expansion step of releasing the pressure and increasing the volume due to the napping force of the discontinuous reinforcing fibers contained in the prepreg (B). The heating and pressurizing step allows the thermoplastic resin contained in the prepreg (B) to soften, making it possible to conform to more complex shapes. Here, the heating and pressurizing process specifically includes methods such as placing the prepreg laminate in a preheated mold and then closing the mold to apply pressure, pressing the prepreg laminate between molds and then raising the mold temperature to heat the prepreg laminate, or heating and pressurizing the prepreg laminate by pressing it between molds while raising the mold temperature. However, it is not limited to these methods. When the state in which the thermoplastic resin of the prepreg (B) is heated to a temperature at which it melts or softens is defined as State 1, and the state in which the prepreg laminate is pressurized is defined as State 2, any process that results in the prepreg laminate being in both State 1 and State 2 is considered the heating and pressurizing process. Furthermore, by including an expansion process, a composite structure with excellent lightness and mechanical properties can be obtained. Here, the expansion process specifically includes methods such as reducing the pressurizing force applied to the upper and lower molds after the heating and pressurizing process to increase the volume of the prepreg (B), or slightly opening the upper and lower molds to relieve the pressure at least temporarily and increase the volume of the prepreg (B). Furthermore, the increase in volume of prepreg (B) during the expansion process only needs to occur in the overlapping region described above.

[0052] The expansion process is preferably carried out in the overlapping region such that Y > Z, where Y is the standard expansion volume and Z is the flow expansion volume of the prepreg (B) as determined below. Here, the standard expansion volume Y is the volume [mm²] of the fiber-reinforced resin structure obtained by heating only the overlapping region of the prepreg (B) contained in the preform until the average temperature inside the prepreg (B) is equal to or greater than the temperature heated in the heating and pressurizing process, and then maintaining that temperature state under atmospheric pressure for 1 hour. 3]. Furthermore, the fluid expansion volume Z is the volume of the layer [mm²] derived from the overlapping region of the prepreg (B) at the completion of the expansion process. 3 This is the case. By manufacturing the composite structure such that Y > Z, it is possible to obtain conformability to complex shapes by utilizing the pressure associated with the expansion of the prepreg (B). To further improve shape conformability, it is preferable that Y / 2 ≥ Z.

[0053] <composite structure> The composite structure of the present invention obtained from the prepreg laminate of the present invention has a layered structure formed by molding the prepreg laminate of the present invention. More preferably, the layer derived from prepreg (B) contains voids. More preferably, the layer derived from prepreg (B) has at least a portion of the contact points where discontinuous reinforcing fibers intersect bonded with a thermoplastic resin, and more preferably contains voids as portions where neither discontinuous reinforcing fibers nor thermoplastic resin are present. [Examples]

[0054] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to these examples.

[0055] <Evaluation Method> (1) Average fiber length and coefficient of variation of reinforcing fibers A 50mm x 50mm prepreg (B) or prepreg (A) was heated in air at 500°C for 1 hour to burn off the resin components. 100 remaining reinforcing fibers were randomly selected, and their lengths were measured to the nearest 1 μm using an optical microscope. The average fiber length was calculated and defined as the average fiber length. The standard deviation of the fiber lengths was calculated from the lengths of the 100 reinforcing fibers, and the coefficient of variation was calculated by dividing the standard deviation by the mean and multiplying the result by 100.

[0056] (2) Two-dimensional orientation angle of prepreg (B) or prepreg (A) The surface of prepreg (B) or prepreg (A) was observed under a microscope, and one reinforcing fiber single filament was randomly selected. The two-dimensional orientation angle between this single filament and another intersecting reinforcing fiber single filament was measured by image observation. The two-dimensional orientation angle was defined as the angle between 0° and 90° (the acute angle) of the two angles formed by the two intersecting reinforcing fiber single filaments. The number of measurements of the two-dimensional orientation angle per reinforcing fiber single filament was n=20. In prepreg (A), the intersecting single filaments were limited to those within the same fiber bundle.

[0057] Similar measurements were performed on four single reinforcing fibers different from those measured above. Of the 100 measured two-dimensional orientation angles, if 80% or more had a two-dimensional orientation angle of 1° or greater, the reinforcing fibers were judged to be single-fiber in shape. Furthermore, if the average of the 100 measured two-dimensional orientation angles was within the range of 30° to 60°, the reinforcing fibers were judged to be randomly oriented, and if it was within the range of 0° to less than 30°, they were judged to be aligned in one direction.

[0058] (3) Sum of cut lengths The sum of the cut lengths provided in one sheet of prepreg (A) or prepreg (B) used in the examples and comparative examples was measured, and 1 m 2 The values ​​were converted to per unit length. The sum of the cut lengths was measured for both surfaces, and the value from the surface with the larger sum of cut lengths was adopted.

[0059] (4) Standard expansion volume Y The prepreg (B) contained in the prepreg laminate used in each example and comparative example was placed in a constant temperature bath set to an ambient temperature of the temperature heated in the heating and pressurizing process + 10°C, held at atmospheric pressure for 1 hour, then removed from the constant temperature bath and cooled to fix its shape, thereby obtaining a molded product derived from prepreg (B). The bottom area of ​​the molded product [mm²] 2 Measure the ] × thickness [mm] and the standard expansion volume Y [mm 3 The result was calculated.

[0060] (5) Molding properties test From the prepreg laminates prepared in each example and comparative example, molded bodies with the shape shown in Figure 4(a) were formed using upper and lower molds. After heating the upper and lower molds to a surface temperature of 180°C, the prepreg laminate was placed on the surface of the lower mold as shown in Figure 5(a), and the upper mold was placed on top of the prepreg laminate and held for 30 seconds. Then, as shown in Figure 5(b), the upper and lower molds were closed so that a pressure of 3 MPa was applied to the prepreg laminate, causing the prepreg laminate to flow (heating and pressurizing process). After holding with the upper and lower molds closed and pressure applied for 5 minutes, the upper and lower molds were opened as shown in Figure 5(c) (expansion process), and the molds were cooled until the temperature of the mold molding surface reached 60°C to obtain a molded body made of a composite structure.

[0061] At the completion of the expansion process, the surface area and thickness of the prepreg (B) portion contained in the molded body were measured, and the surface area [mm²] was determined. 2 Measure the ] × thickness [mm] and the fluid expansion volume Z [mm 3 The result was calculated.

[0062] Furthermore, the core filling ratio was calculated as the ratio of (surface area of ​​prepreg (B)-derived component) / (surface area of ​​prepreg (A)-derived component) in the molded body. The surface area of ​​the prepreg (B)-derived component or the prepreg (A)-derived component refers to the area of ​​the prepreg (B)-derived component or the prepreg (A)-derived component contained in the molded body that is aligned in the in-plane direction. If the molded body is a flat plate shape, the projected area in the thickness direction can be used, and if it is a three-dimensional shape, it can be calculated using CAD software, for example. In this embodiment, the surface area was calculated by modeling the shape of the molded body using general-purpose CAD software. The closer the core filling ratio is to 1, the more prepreg (A) and prepreg (B) deform to the same extent and follow the shape in a balanced manner, meaning that the shape-following ability is excellent.

[0063] Furthermore, the maximum thickness t of the corner 9 with thickness variation shown in Figure 4(a) was measured to evaluate the ability to follow thickness changes. In the molded body, t was measured at a total of four locations, and the average value of these measurements was taken as the average thickness of the thicker section. Due to the mold design, the maximum thickness of the corner is 4 mm. The closer the average value of the measured thickness is to 4 mm, the more accurately the molding can be evaluated as being performed to the designed dimensions, and the better the ability to follow thickness changes.

[0064] Furthermore, a 150 mm square test specimen was prepared by cutting out the top surface portion 10 shown in Figure 4(b) from the molded body shown in Figure 4(a). This specimen was placed on a square-shaped jig with sides of 150 mm, a width of 10 mm, and a height of 10 mm. Using a mechanical testing machine, a load of up to 100 N was applied to the position indicated by the load application section 8 with an indenter having a circular surface with a diameter of 20 mm. The displacement of the indenter (compression displacement) was measured and used as an indicator of the rigidity of the molded body. A smaller compression displacement is considered to indicate superior mechanical properties.

[0065] (6) Measurement of the orientation angle of the fiber bundles contained in the prepreg (A) The surface of the target fiber bundle was observed under a microscope, and one reinforcing fiber single filament was randomly selected. Furthermore, a virtual reference line was set on the prepreg, and the angle between this reference line and the randomly selected reinforcing fiber single filament was measured. The same measurement was performed on a total of 100 reinforcing fibers from the same fiber bundle, and the average of these angles was taken as the orientation angle of the target fiber bundle.

[0066] <Prepreg fabrication> [Thermoplastic resin sheet (I)] This material consists of 50% by weight of unmodified polypropylene resin (Prime PolyPro® J105G, manufactured by Prime Polymer Co., Ltd.) and 50% by weight of acid-modified polypropylene resin (Admer QB510, manufactured by Mitsui Chemicals, Inc.), with a basis weight of 100 g / m². 2 A thermoplastic resin sheet (I) was fabricated.

[0067] [Discontinuous reinforced fiber web (I)] A continuous PAN-based carbon fiber bundle with a total of 12,000 single filaments, having a tensile strength of 4900 MPa and a tensile modulus of 230 GPa, was cut to 6 mm using a cartridge cutter to obtain discontinuous reinforced fibers. A dispersion liquid with a concentration of 0.1 wt% consisting of water and a surfactant (Nacalai Tex Co., Ltd., polyoxyethylene lauryl ether (trade name)) was prepared, and a discontinuous reinforced fiber web (I) was manufactured from this dispersion liquid and the above discontinuous reinforced fibers using a discontinuous reinforced fiber web manufacturing apparatus. The manufacturing apparatus consists of a cylindrical container with a diameter of 1000 mm and an opening cock at the bottom of the container serving as a dispersion tank, and a linear transport section (inclination angle of 30°) connecting the dispersion tank and the papermaking tank. An agitator is attached to the opening on the top surface of the dispersion tank, and the discontinuous reinforced fibers and dispersion liquid (dispersion medium) can be introduced through the opening. The papermaking tank is a tank equipped with a mesh conveyor with a papermaking surface of 500 mm width at the bottom, and a conveyor capable of transporting papermaking substrates is connected to the mesh conveyor. Papermaking was performed with a discontinuous reinforcement fiber concentration of 0.05% by weight in the dispersion. The resulting discontinuous reinforcement fibers were dried in a 200°C drying oven for 30 minutes. The resulting discontinuous reinforcement fiber web (I) had a width of 500 mm, a length of 500 mm, and a basis weight of 100 g / m². 2 That was the case.

[0068] [Resin-impregnated substrate (I)] Using a discontinuous reinforced fiber web (I) and a thermoplastic resin sheet (I), a resin-impregnated substrate (I) was prepared by laminating them in the order of [thermoplastic resin sheet (I) / discontinuous reinforced fiber web (I) / thermoplastic resin sheet (I)] and impregnating the discontinuous reinforced fiber web (I) with thermoplastic resin by applying a pressure of 5 MPa at a temperature of 230°C for 2 minutes.

[0069] [Prepreg (BI)] By pressing a rotating blade against the resin-impregnated substrate (I), a prepreg (BI) was obtained by inserting cuts in a regular pattern as shown in Figure 2(b). The cuts were provided across the entire surface of the prepreg (BI) and penetrated in the thickness direction of the prepreg (BI). 2 The sum of the cut lengths per unit area, Cb, was changed in each example and comparative example as shown in Table 1.

[0070] According to (2) above, when the in-plane two-dimensional orientation angle of the prepreg (BI) was measured, 90% of the fibers had a two-dimensional orientation angle of 1° or more. Furthermore, the average value of the two-dimensional orientation angle was 45°. In other words, the reinforcing fibers were monofilamentous and randomly oriented.

[0071] [Continuous fiber prepreg (I)] An epoxy resin composition was prepared by kneading epoxy resin (Epicoat® 828: 30 parts by weight, Epicoat® 1001: 35 parts by weight, Epicoat® 154: 35 parts by weight, manufactured by Japan Epoxy Resin Co., Ltd.) with 5 parts by weight of thermoplastic resin polyvinyl formal (Vinirec® K, manufactured by Chisso Corporation) in a kneader to uniformly dissolve the polyvinyl formal. Then, 3.5 parts by weight of the curing agent dicyandiamide (DICY7, manufactured by Japan Epoxy Resin Co., Ltd.) and 4 parts by weight of the curing accelerator 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU99, manufactured by Hodogaya Chemical Co., Ltd.) were kneaded in a kneader to prepare an uncured epoxy resin composition. This epoxy resin composition was applied to a 100 μm thick release paper treated with silicone using a reverse roll coater to produce a resin film. Next, a resin film was placed on both sides of the aforementioned PAN-based continuous carbon fiber bundles, which were arranged in one direction, and the resin was impregnated by heating and pressurizing to produce a continuous fiber prepreg (I) with a carbon fiber weight of 125 g / m2 per unit area, a fiber volume content Vf of 55%, and a thickness of 0.125 mm. The two-dimensional orientation angle of the continuous fiber prepreg (I) was measured according to the method described in (2), and the average value of the two-dimensional orientation angle was 2°.

[0072] [Prepreg (AI)] Next, a rotary blade with multiple blades positioned at predetermined locations on the continuous fiber prepreg (I) was pressed against the prepreg to insert cuts that penetrate the prepreg (I), forming fiber bundles and obtaining prepreg (AI). The rotary blade used had blades arranged alternately with angles of +14° and -14° to the direction of travel, and the blades were positioned so that all the reinforcing fibers of the continuous fiber prepreg (I) would be cut. 2 The sum of the cut lengths per unit area, Ca, was changed in each example and comparative example as shown in Table 1. In addition, the orientation direction of any fiber bundle contained in the prepreg (AI) was measured using the method described in (6), and the orientation direction of a total of 20 other comparative fiber bundles was also measured. When the angle difference between the orientation direction of the arbitrarily selected fiber bundle and the orientation direction of the comparative fiber bundles was calculated, it was found to be 5° or less in all cases, so it was determined that the fiber bundles contained in the prepreg (AI) are aligned in one direction.

[0073] [Prepreg (AII)] A prepreg (AII) was fabricated by cutting a continuous fiber prepreg (I) into fiber bundles 3 mm wide and 30 mm long to obtain chopped prepregs. These chopped prepregs were arranged so that the fiber directions of each chopped prepreg were randomly oriented, and then vacuum-sealed at 70°C for 1 minute. The orientation direction of any fiber bundle contained in prepreg (AII) was measured using the method described in (6), and the orientation direction of a total of 20 other comparative fiber bundles was similarly measured. The angular difference from the orientation direction of the aforementioned arbitrary fiber bundle was calculated, confirming that the fiber bundles are oriented in eight directions.

[0074] (Example 1) The Ca cuts inserted into the prepreg (AI) are 400 mm 2 The Cb in the cuts inserted into the prepreg (BI) is 200 mm 2The prepreg (BI) and prepreg (AI) were both cut to dimensions of 150 mm x 150 mm, and a prepreg laminate (I) was obtained by stacking them in the order of (prepreg (AI) / prepreg (AI) / prepreg (BI) / prepreg (AI) / prepreg (AI)). At this time, adjacent prepregs (AI) were stacked so that their fiber directions intersected at 90°, and in the overlapping region of adjacent prepregs (AI) and prepregs (BI), when the cut patterns of prepregs (AI) and prepregs (BI) were projected in the thickness direction, at least a portion of the cuts of both intersected.

[0075] The prepreg laminate (I) was used as a preform, and the moldability test described in (5) was performed. At this time, the expansion process was carried out so that the distance h between the upper and lower molds was 2.0 mm, as shown in Figure 5(c). The results are shown in Table 1.

[0076] (Example 2) The Ca cuts inserted into the prepreg (AI) are 200 mm 2 The cuts in the prepreg (BI) were made with 20 mm of Cb. 2 A molded article consisting of a prepreg laminate and a composite structure was obtained in the same manner as in Example 1, except for the difference described above.

[0077] (Example 3) The Ca cuts inserted into the prepreg (AI) are 200 mm 2 The cuts in the prepreg (BI) were made of 40 mm Cb. 2 A molded article consisting of a prepreg laminate and a composite structure was obtained in the same manner as in Example 1, except for the difference described above.

[0078] (Example 4) The cut length of Ca inserted into the prepreg (AI) is 200 mm 2 The cut length of Cb inserted into the prepreg (BI) is 100 mm 2 A molded article consisting of a prepreg laminate and a composite structure was obtained in the same manner as in Example 1, except for the difference described above.

[0079] (Example 5-1) The cut length of Ca inserted into the prepreg (AI) is 200 mm 2 The cut length of Cb inserted into the prepreg (BI) is 200 mm 2 A molded article consisting of a prepreg laminate and a composite structure was obtained in the same manner as in Example 1, except for the difference described above.

[0080] (Example 5-2) In Figure 5(c), a molded body made of a composite structure was formed in the same manner as in Example 5-1, except that the expansion process was carried out so that the distance h between the upper and lower molds was 2.5 mm. (Example 5-3) In Figure 5(c), a molded body made of a composite structure was formed in the same manner as in Example 5-1, except that the expansion process was carried out so that the distance h between the upper and lower molds was 1.7 mm.

[0081] (Example 6) The Ca cuts inserted into the prepreg (AI) are 200 mm 2 The cut length of Cb inserted into the prepreg (BI) is 400 mm 2 A molded article consisting of a prepreg laminate and a composite structure was obtained in the same manner as in Example 1, except for the difference described above.

[0082] (Example 7) The cut length of Ca inserted into the prepreg (AI) is 200 mm 2 The cut length of Cb inserted into the prepreg (BI) is 800 mm 2 A molded article consisting of a prepreg laminate and a composite structure was obtained in the same manner as in Example 1, except for the difference described above.

[0083] (Example 8) A molded body consisting of a prepreg laminate and a composite structure was obtained in the same manner as in Example 5-1, except that the arrangement of cuts contained in adjacent prepregs (AI) and prepregs (BI) was made the same, and after initially arranging them so that all of their cuts overlapped, they were slightly offset in the in-plane direction so that their cuts did not completely intersect.

[0084] (Example 9) A molded article consisting of a prepreg laminate and a composite structure was obtained in the same manner as in Example 5, except that prepreg (AII) was used instead of prepreg (AI). The sum Ca of the cut lengths of prepreg (A) was not measured because there were no cuts.

[0085] (Example 10) The Ca cuts inserted into the prepreg (AI) are 800 mm 2 The cuts in the prepreg (BI) were made of 40 mm Cb. 2 A molded article consisting of a prepreg laminate and a composite structure was obtained in the same manner as in Example 1, except for the difference described above.

[0086] (Example 11) The Ca cuts inserted into the prepreg (AI) are 100 mm 2 The Cb in the cuts inserted into the prepreg (BI) was 800 mm 2 A molded article consisting of a prepreg laminate and a composite structure was obtained in the same manner as in Example 1, except for the difference described above.

[0087] (Comparative Example 1) A molded body consisting of a composite structure was formed in the same manner as in Example 5-1, except that the resin-impregnated substrate (I) before the cuts were inserted was used instead of the prepreg (BI). As a result, the core filling rate was extremely low due to insufficient shape conformability of the resin-impregnated substrate (I), and the shape conformability of the corners was also extremely low because the resin-impregnated substrate (I) did not conform to the shape and became rigid under pressure. Since the shape differed significantly from that shown in Figure 4(a), the displacement under compression was not measured.

[0088] (Comparative Example 2) A molded body consisting of a composite structure was formed in the same manner as in Example 5-1, except that continuous fiber prepreg (I) before the insertion of cuts was used instead of prepreg (AI). Since it was a continuous fiber, the coefficient of variation of the fiber length was not measured. As a result, the continuous fiber prepreg (I) on the surface did not follow the mold shape, and large wrinkles were observed on the surface. In addition, because the continuous fiber prepreg (I) did not follow the mold shape and became rigid under pressure, the shape-following ability of the corners was also significantly reduced. Since it differed greatly from the shape in Figure 4(a), the displacement under compression was not measured.

[0089] [Table 1] [Explanation of Symbols]

[0090] 1: Cut 2: Cutting area 3: Prepreg (B) 4: Cutting unit 5a, 5b1~5b5: Reinforced fiber single yarn 6: Two-dimensional orientation angle 7: Composite structure 8: Load application section 9: Corners with changes in thickness 10:Top section t: Maximum thickness of the corner with thickness variation 11: Upper mold 12: Lower mold 13: Prepreg laminate h: Distance between upper and lower molds

Claims

1. A prepreg (A) in which discontinuous reinforcing fibers are impregnated with a thermosetting resin or thermoplastic resin, A prepreg laminate comprising a prepreg (B) in which discontinuous reinforcing fibers are impregnated with a thermoplastic resin, laminated adjacently to a prepreg (A), wherein the prepreg (A) is arranged on at least one surface, A combination of at least a portion of adjacent prepregs (A) and prepregs (B) forms an overlapping region that satisfies at least one of the following conditions (1) and (2): The discontinuous reinforcing fibers contained in the prepreg (B) are in a web form. The prepreg (A) has multiple cuts, and the discontinuous reinforcing fibers contained in the prepreg (A) are formed when continuous reinforcing fibers, which are arranged in one direction, are cut by these cuts, thereby forming fiber bundles that are also arranged in one direction. The prepreg (B) has a plurality of cuts that cut at least a portion of the web-shaped discontinuous reinforcing fibers, The overlapping region is formed by the overlap of the cut region in the prepreg (A) where the cut is formed and the cut region in the prepreg (B) where the cut is formed. In the overlapping region, the sum of the cut lengths per 1 m² of prepreg (A) and prepreg (B) is calculated as Ca [mm / m²]. ２ ], Cb[m / m ２ A prepreg laminate that satisfies 0.1 ≤ Cb / Ca < 5 when ]. (1) The coefficient of variation of the fiber length of the discontinuous reinforcing fibers contained in prepreg (B) is greater than the coefficient of variation of the fiber length of the discontinuous reinforcing fibers contained in prepreg (A). (2) Prepreg (B) has multiple cuts that cut the discontinuous reinforcing fibers contained in prepreg (B), and the average value of the two-dimensional orientation angles of the discontinuous reinforcing fibers contained in prepreg (B) is greater than the average value of the two-dimensional orientation angles of the discontinuous reinforcing fibers contained in prepreg (A).

2. The prepreg laminate according to claim 1, wherein in the overlapping region, the average fiber length of the discontinuous reinforcing fibers contained in prepreg (A) is longer than the average fiber length of the discontinuous reinforcing fibers contained in prepreg (B).

3. The prepreg laminate according to claim 1 or 2, wherein in the overlapping region, 50% or more of the discontinuous reinforcing fibers contained in prepreg (B), in terms of the number of fibers, have a fiber length less than or equal to the average fiber length of the reinforcing fibers contained in prepreg (A).

4. In the aforementioned cut region, the cuts in the prepreg (A) and the prepreg (B) are formed in a certain pattern when viewed from above. The prepreg laminate according to claim 1, wherein in the overlapping region, when the cut pattern of the prepreg (A) and the cut pattern of the prepreg (B) are projected in the thickness direction, at least a portion of the cuts of both intersects.

5. The prepreg laminate according to any one of claims 1 to 4, wherein the prepreg (A) and the prepreg (B) are stacked symmetrically with respect to the center of the stacking direction of the prepreg laminate.

6. A method for manufacturing a composite structure, comprising heating and pressurizing a preform containing a prepreg laminate according to any one of claims 1 to 5.

7. A heating and pressurizing step in which the thermoplastic resin of the prepreg (B) is heated and pressurized to a temperature at which it melts or softens, An expansion step to relieve pressure and increase the volume of the prepreg (B) by the napping force of the discontinuous reinforcing fibers contained in the prepreg (B), A method for manufacturing a composite structure according to claim 6, comprising having the above characteristics.

8. A method for manufacturing a composite structure according to claim 7, wherein the expansion process is performed such that Y > Z, where Y is the standard expansion volume of the overlapping region of the prepreg (B) determined as follows, and Z is the flow expansion volume of the overlapping region of the prepreg (B). Standard expansion volume Y: The volume [mm²] of the fiber-reinforced resin structure obtained by heating only the overlapping region of the prepreg (B) until the average internal temperature is equal to or higher than the temperature reached in the heating and pressurizing process, and then maintaining that state under atmospheric pressure for one hour. ３ ]. Flow expansion volume Z: Volume of the layer derived from the overlapping region of the prepreg (B) at the completion of the expansion process [mm²] ３ ].

9. A composite structure having a layered structure formed by molding a prepreg laminate according to any one of claims 1 to 5.

10. The composite structure according to claim 9, wherein the layer derived from the prepreg (B) contains voids.

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