Fiber-reinforced plastic and method for producing fiber-reinforced plastic

Abstract

The present invention pertains to a fiber-reinforced plastic that has, as at least one of the surface layers in the thickness direction thereof, a layer containing reinforced fibers and a matrix in which a thermosetting resin and a thermoplastic resin are integrated. The reinforced fibers form discontinuous reinforced fiber bundles randomly stacked or discontinuous reinforced fiber bundles arranged in one direction. A portion of the discontinuous reinforced fiber bundles is in contact with both of the thermosetting resin and the thermoplastic resin. The thermoplastic resin is exposed in at least a portion of the surface of the surface layer.

Description

[Technical Field]

[0001] The present invention relates to a fiber-reinforced plastic and a method for producing the same. [Background technology]

[0002] Fiber-reinforced plastics, which use a thermosetting or thermoplastic resin as a matrix and combine it with reinforcing fibers such as carbon fiber or glass fiber, are lightweight yet have excellent mechanical properties such as strength and rigidity, as well as heat resistance and corrosion resistance. For this reason, fiber-reinforced plastics have been applied in many fields, including aerospace, automobiles, railways, ships, civil engineering and construction, and sporting goods.

[0003] However, fiber-reinforced plastics are not suitable for manufacturing parts or structures having complex shapes in a single molding process, and for the above-mentioned applications, it is necessary to manufacture a member made of fiber-reinforced plastic and then integrate it with other members of the same or different types.Methods for integrating fiber-reinforced plastics with other members of the same or different types include mechanical joining methods using bolts, rivets, screws, etc., and joining methods using adhesives.

[0004] Mechanical joining methods require pre-processing of the joining parts, such as drilling holes, which leads to longer manufacturing processes and increased manufacturing costs, and also has the problem of material strength being reduced due to the need to drill holes.Joining methods that use adhesives also require adhesive preparation and a bonding process that includes applying the adhesive, as well as a curing process, which leads to longer manufacturing processes and also has the problem of not being able to achieve sufficient reliability in terms of joint strength.

[0005] Fiber-reinforced plastics that use a thermoplastic resin as the matrix resin can be joined to components that use other thermoplastic resins by welding, which makes it relatively easy to simplify the process. For example, Patent Document 1 discloses a fiber-reinforced resin laminate in which a thermosetting resin layer and a thermoplastic resin layer form an uneven boundary surface inside a reinforcing fiber bundle, and describes that a bonded body with excellent bonding strength can be obtained by joining the laminate to other components by welding via the thermoplastic resin layer. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2004 / 060658 Summary of the Invention [Problem to be solved by the invention]

[0007] In the laminate using a thermoplastic resin described in Patent Document 1, the interface between the thermosetting resin and the thermoplastic resin is located inside the reinforcing fiber bundle. Therefore, the reinforcing fibers bear the load, suppressing interfacial peeling between the thermosetting resin and the thermoplastic resin, while at the same time providing excellent bonding strength when welded to another member. However, this laminate was not necessarily suitable for applications where shape conformability was prioritized over strength.

[0008] An object of the present invention is to provide a fiber-reinforced plastic that can be joined to another component by welding via a thermoplastic resin, and that has excellent joining strength with the other component while also having excellent shape-following ability. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention has the following configuration. <1> A fiber-reinforced plastic having a layer containing reinforcing fibers and a matrix in which a thermosetting resin and a thermoplastic resin are integrated as at least one surface layer in the thickness direction, The reinforcing fibers form discontinuous reinforcing fiber bundles that are randomly stacked or that are unidirectionally aligned, A portion of the discontinuous reinforcing fiber bundles is in contact with both the thermosetting resin and the thermoplastic resin, The fiber-reinforced plastic has the thermoplastic resin exposed on at least a portion of the surface of the surface layer. <2> In the surface layer, an interface is formed between a region containing the thermosetting resin as a main component and a region containing the thermoplastic resin as a main component. <1> The fiber reinforced plastic according to claim 1. <3> In the surface layer, the thermoplastic resin has a continuous region from the surface in a thickness direction, The maximum thickness of the part where the thermoplastic resin contacts the discontinuous reinforcing fiber bundles in the region is 10 μm or more. <1> or <2> The fiber reinforced plastic according to claim 1. <4> In the surface layer, the content of the reinforcing fibers is 15% by volume or more and 70% by volume or less, <1> ~ <3> 10. The fiber-reinforced plastic according to any one of the above items. <5> In the surface layer, the average fiber length of the reinforcing fibers is in the range of 5 mm to 100 mm. <1> ~ <4> 10. The fiber-reinforced plastic according to any one of the above items. <6> In the surface layer, the reinforcing fiber is at least one selected from the group consisting of carbon fiber and glass fiber. <1> ~ <5> 10. The fiber-reinforced plastic according to any one of the above items. <7> In the surface layer, the presence ratio of voids in contact with the longitudinal ends of the discontinuous reinforcing fiber bundles is 5% by area or less. <1> ~ <6> 10. The fiber-reinforced plastic according to any one of the above items. <8> In the surface layer, the longitudinal impregnation distance is 20 μm or more. <1> ~ <7> 10. The fiber-reinforced plastic according to any one of the above items. <9> In the surface layer, the thermoplastic resin is present between the discontinuous reinforcing fiber bundles. <1> ~ <8> 10. The fiber-reinforced plastic according to any one of the above items. <10> the thermoplastic resin occupies the spaces between any adjacent discontinuous fiber reinforcement bundles; <9> The fiber reinforced plastic according to claim 1. <11> The discontinuous reinforcing fiber bundles, the thermoplastic resin, and the thermosetting resin are included in both surface layers in the thickness direction, The thermoplastic resin is exposed on the surfaces of both of the surface layers. <1> ~ <10> 10. The fiber-reinforced plastic according to any one of the above items. <12> At least a part of the discontinuous reinforcing fiber bundles constituting the fiber reinforced plastic is oriented in the out-of-plane direction, <1> ~ <11> 10. The fiber-reinforced plastic according to any one of the above items. <13> <1> ~ <12> A method for producing a fiber reinforced plastic according to any one of the above, Step 1: impregnating a reinforcing fiber bundle with a thermosetting resin; Step 2: impregnating the reinforcing fiber bundle with a thermoplastic resin; Step 3: cutting the reinforcing fiber bundles to form discontinuous reinforcing fiber bundles; A step 4 of laminating a required number of substrates constituting a fiber reinforced plastic so that the thermoplastic resin is exposed on at least one surface in the thickness direction; and step 5 of molding the fiber reinforced plastic by heating and pressurizing, The method for producing a fiber-reinforced plastic, wherein the step 5 is carried out after the steps 1 to 4 are carried out, or is carried out simultaneously with the step 2 after the steps 1, 3, and 4 are carried out, or is carried out simultaneously with the step 1 after the steps 2, 3, and 4 are carried out. <14> In the surface layer where the thermoplastic resin is exposed, the longitudinal ends of the discontinuous reinforcing fiber bundles are allowed to flow so as to come into contact with the thermosetting resin or the thermoplastic resin, <13> A method for producing a fiber reinforced plastic according to claim 1. <15> In step 6, In the surface layer where the thermoplastic resin is exposed, at least a part of the discontinuous reinforcing fiber bundles is in contact with both the thermosetting resin and the thermoplastic resin, And at least one of the reinforcing fibers constituting the reinforcing fiber bundle and the thermoplastic resin are caused to flow so as to be in continuous contact with each other in the longitudinal direction from the longitudinal end of the reinforcing fiber. <13> or <14> A method for producing a fiber reinforced plastic according to claim 1. [Effects of the Invention]

[0010] The fiber-reinforced plastic of the present invention has a thermoplastic resin exposed on at least a portion of the surface of the surface layer, allowing it to be joined to another member by welding via the thermoplastic resin. Furthermore, because a portion of the discontinuous reinforcing fiber bundles is in contact with both the thermosetting resin and the thermoplastic resin, peeling at the interface between the thermosetting resin and the thermoplastic resin is unlikely to occur. Furthermore, because the reinforcing fibers are discontinuous reinforcing fiber bundles, they have excellent shape conformability, making them particularly useful in applications where both strength and shape conformability are required. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic plan view of one embodiment of a fiber-reinforced plastic of the present invention. [Figure 2] FIG. 2 is a cross-sectional schematic view of one embodiment of the fiber-reinforced plastic of the present invention. [Figure 3] FIG. 3 is a schematic diagram of one embodiment of a cut prepreg that can be used when producing the fiber reinforced plastic of the present invention. [Figure 4] FIG. 4 is a cross-sectional schematic diagram of one embodiment of the fiber reinforced plastic of the present invention, which helps to explain the method for measuring the maximum impregnation distance. [Figure 5] FIG. 5 is a cross-sectional schematic view of one embodiment of the fiber reinforced plastic of the present invention. [Figure 6] FIG. 6 is a cross-sectional schematic view of one embodiment of the fiber reinforced plastic of the present invention. [Figure 7] FIG. 7 is a cross-sectional schematic diagram of one embodiment of the fiber reinforced plastic of the present invention, and helps to explain the method for measuring the roughness average height Rc. [Figure 8] FIG. 8 is a cross-sectional schematic diagram of one embodiment of the fiber reinforced plastic of the present invention, and helps to explain the method for measuring the longitudinal impregnation distance. [Figure 9] FIG. 9 shows an example of the fiber reinforced plastic of the present invention, and illustrates an example of the shape of the fiber reinforced plastic of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] [Fiber reinforced plastic] The fiber-reinforced plastic of the present invention will be described below with reference to the drawings as appropriate, but the drawings are used for convenience to facilitate understanding of the present invention and do not limit the present invention in any way. In this specification, the cross section of a fiber-reinforced plastic refers to a cross section cut parallel to the thickness direction, unless otherwise specified.

[0013] The fiber reinforced plastic of the present invention is a fiber reinforced plastic having a layer containing reinforcing fibers and a matrix in which a thermosetting resin and a thermoplastic resin are integrated as at least one surface layer in the thickness direction, The reinforcing fibers form discontinuous reinforcing fiber bundles that are randomly stacked or that are unidirectionally aligned, A portion of the discontinuous reinforcing fiber bundles is in contact with both the thermosetting resin and the thermoplastic resin, The thermoplastic resin is exposed on at least a portion of the surface of the surface layer.

[0014] The fiber-reinforced plastic of the present invention contains a plurality of discontinuous reinforcing fiber bundles as reinforcing fibers. The discontinuous reinforcing fiber bundles are composed of a plurality of discontinuous reinforcing fibers. The bundles of discontinuous reinforcing fibers allow the fiber-reinforced plastic to have excellent rigidity.

[0015] Examples of reinforcing fibers include carbon fibers, glass fibers, metal fibers, aromatic polyamide fibers, polyaramid fibers, alumina fibers, silicon carbide fibers, boron fibers, and basalt fibers. Among these, reinforcing fibers such as carbon fibers and glass fibers are preferred from the viewpoints of elastic modulus, strength, and practicality. These reinforcing fibers may be used alone or in combination of two or more types as appropriate.

[0016] As the reinforcing fiber, carbon fiber is particularly preferably used because of its low specific gravity, high strength, and high elastic modulus. Commercially available carbon fiber products include, for example, Torayca (registered trademark) T800G-24K, Torayca (registered trademark) T800S-24K, Torayca (registered trademark) T700G-24K, Torayca (registered trademark) T700S-24K, Torayca (registered trademark) T300-3K, and Torayca (registered trademark) T1100G-24K (all manufactured by Toray Industries, Inc.).

[0017] These reinforcing fibers may be surface-treated, such as by coating with a metal, by treatment with a coupling agent, by treatment with a sizing agent, or by adhesion of an additive.

[0018] In the present invention, as shown in FIG. 1, discontinuous reinforcing fiber bundles 2 can be present in a randomly stacked state in the surface layer of the fiber-reinforced plastic. One example of a method for obtaining the surface layer of the fiber-reinforced plastic of the present invention is a method in which reinforcing fiber bundles are previously cut and the resulting discontinuous reinforcing fiber bundles are deposited on a carrier to form a stacked state, and then a substrate impregnated with a thermosetting resin and a thermoplastic resin is molded. One example of randomly stacked discontinuous reinforcing fiber bundles in the present invention is sheet molding compound (SMC). Randomly stacking the discontinuous reinforcing fiber bundles can provide excellent shape conformability, which is advantageous in applications where shape conformability is relatively prioritized over strength.

[0019] In the present invention, the discontinuous reinforcing fiber bundles 2 can be stacked randomly. Here, "the discontinuous reinforcing fiber bundles are stacked randomly" means that, when the surface layer of the fiber-reinforced plastic of the present invention is viewed in plan, the orientation direction of one discontinuous reinforcing fiber bundle randomly selected from those having overlapping portions of discontinuous reinforcing fiber bundles is used as a reference, and the orientation directions of 20 discontinuous reinforcing fiber bundles selected at random from the one discontinuous reinforcing fiber bundle are intersected in a plane (when the discontinuous reinforcing fiber bundles do not intersect, the angle formed by the extension lines of the orientation directions of the discontinuous reinforcing fiber bundles intersecting in a plane) and the smaller of these angles (hereinafter, this may be referred to as "two-dimensional orientation angle") is measured and the average value is 10 degrees or more and 80 degrees or less.

[0020] The orientation direction projected onto the plane of the discontinuous reinforcing fiber bundle is determined by selecting one reinforcing fiber contained in the discontinuous reinforcing fiber bundle visible in plan view and determining the direction of a straight line connecting the visible longitudinal ends of the selected reinforcing fiber. The selected reinforcing fiber is arbitrary, but it is preferable that it is located near the center of the discontinuous reinforcing fiber bundle in the fiber orthogonal direction, and that the surrounding reinforcing fibers contained in the same discontinuous reinforcing fiber bundle are approximately parallel to the selected reinforcing fiber. When the extension lines of the orientation directions of the discontinuous reinforcing fiber bundles do not intersect, the two-dimensional orientation angle is determined to be 0 degrees.

[0021] In the present invention, the average value of the two-dimensional orientation angle is more preferably 30 degrees or more and 60 degrees or less, and even more preferably 40 degrees or more and 50 degrees or less, and the closer to the ideal angle of 45 degrees, the more preferable.

[0022] In the present invention, the discontinuous reinforcing fiber bundles in the surface layer can be oriented in one direction. When the discontinuous reinforcing fiber bundles are oriented in one direction, the strength of the fiber-reinforced plastic can be improved, which is advantageous in applications where strength is prioritized over shape conformability. Here, "the discontinuous reinforcing fiber bundles are oriented in one direction" means that the average value of the two-dimensional orientation angle is equal to or greater than 0 degrees and less than 10 degrees.

[0023] One example of a method for obtaining the surface layer of the fiber-reinforced plastic of the present invention is a method in which a substrate is formed by cutting at least a portion of the reinforcing fiber bundles contained in a prepreg in which the reinforcing fibers are aligned in one direction, and forming the discontinuous reinforcing fiber bundles. An example of such a prepreg is a cut prepreg 7 as shown in Figure 3.

[0024] When using a slit prepreg 7, the slits inserted in the prepreg may be slits perpendicular to the longitudinal direction 9 of the reinforcing fiber bundle or oblique slits, or may be paired slits 8 that form an angle θ = ±α with the longitudinal direction 9 of the reinforcing fiber bundle, as shown in Figure 3. The shape of the slits and the shape of the discontinuous reinforcing fiber bundles are not particularly limited. Furthermore, the slit prepreg may have slits parallel to the reinforcing fibers that divide the fiber bundles in the width direction, in addition to the slits that divide the reinforcing fibers in the longitudinal direction as shown in Figure 3.

[0025] The fiber-reinforced plastic of the present invention has a surface layer containing reinforcing fibers forming discontinuous reinforcing fiber bundles existing in the above-described state and a matrix in which a thermosetting resin and a thermoplastic resin are integrated. Furthermore, a portion of the discontinuous reinforcing fiber bundles is in contact with both the thermosetting resin and the thermoplastic resin, and the thermoplastic resin is present on the surface of the surface layer (hereinafter, this may be referred to as "the thermoplastic resin is exposed").

[0026] This allows for good welding of the same or different types of components via the thermoplastic resin, which reduces the time required for the joining process compared to fiber-reinforced plastics, which consist only of thermosetting resin and reinforcing fibers, and enables the molding of structural components to be done more quickly.

[0027] Examples of shapes of the fiber-reinforced plastic of the present invention include, but are not limited to, a flat plate shape with uneven sides, a shape with a flat portion and a curved portion such as an L-shaped member, and a shape in which at least a portion of the discontinuous reinforcing fiber bundles are oriented in the out-of-plane direction, such as a rib shape or uneven shape.

[0028] In addition, the term "discontinuous reinforcing fiber bundles are oriented in the out-of-plane direction" means that when a discontinuous reinforcing fiber bundle in a surface layer is arranged horizontally, there exists a combination in which a part of another discontinuous reinforcing fiber bundle in the same surface layer makes an angle of 5 degrees or more with respect to the horizontal.

[0029] In the fiber-reinforced plastic of the present invention, the average fiber length of the reinforcing fibers constituting the discontinuous reinforcing fiber bundles in the surface layer is preferably 5 mm or more and 100 mm or less. Having an average fiber length of 5 mm or more allows the reinforcing fibers present at the interface between the thermosetting resin and the thermoplastic resin to sufficiently bear the load. Therefore, the stress applied to the interface between the thermosetting resin and the thermoplastic resin is reduced, and as a result, interfacial peeling is suppressed, making it easier to achieve the effect of improving the bonding strength. Furthermore, having an average fiber length of 100 mm or less results in excellent shape-following ability when the fiber-reinforced plastic is molded.

[0030] In addition, it is preferable that the fiber lengths of the reinforcing fibers constituting each of the discontinuous reinforcing fiber bundles contained in the surface layer are substantially the same. By making the fiber lengths substantially the same, it is possible to suppress variation in the mechanical properties of the fiber-reinforced plastic of the present invention.

[0031] Here, "the fiber lengths are substantially the same" means that the proportion of the number of reinforcing fibers that are 10 mm or more longer or shorter than the average fiber length (hereinafter sometimes referred to as "fiber bundle length") of the reinforcing fibers constituting one discontinuous reinforcing fiber bundle contained in the surface layer is 10% or less of all the reinforcing fibers contained in the discontinuous reinforcing fiber bundle. The closer the proportion of the number of reinforcing fibers is to 0%, the better; however, in the manufacturing process, misalignment of the substrate, chipping of the blade, etc. may occur, making it impossible to cut as designed, and the proportion of the number of reinforcing fibers may become greater than 0%.

[0032] Furthermore, it is more preferable that the average fiber lengths of all discontinuous reinforcing fiber bundles contained in the surface layer, excluding those in contact with the side surfaces, are substantially the same. The term "substantially the same average fiber length" means that the proportion of discontinuous reinforcing fiber bundles having a fiber bundle length 10 mm or more longer or shorter than the average fiber bundle length among the discontinuous reinforcing fiber bundles contained in the surface layer is 10% or less. The proportion of discontinuous reinforcing fiber bundles is preferably as close to 0% as possible; however, in the manufacturing process, misalignment of the substrate, chipping of the blade, etc. may occur, preventing cutting as designed, and the proportion of discontinuous reinforcing fiber bundles may be greater than 0%.

[0033] In the fiber-reinforced plastic of the present invention, the thermoplastic resin may be exposed on one or both surfaces. That is, the fiber-reinforced plastic of the present invention may have layers containing discontinuous reinforcing fiber bundles, a thermoplastic resin, and a thermosetting resin on both surface layers in the thickness direction, and the thermoplastic resin may be exposed on both surface layers.

[0034] Hereinafter, in the fiber reinforced plastic of the present invention, the surface including the portion where the thermoplastic resin contained in the surface layer is exposed will be referred to as the "joint surface." Note that when the thermoplastic resin is exposed on both sides of the fiber reinforced plastic, both sides will be the "joint surfaces."

[0035] The proportion of the thermoplastic resin on the surface of the joining surface is not particularly limited, and the thermoplastic resin may be exposed over the entire joining surface or only a portion of the joining surface. The greater the proportion of the thermoplastic resin exposed on the joining surface, the larger the area available for joining, and therefore an increase in joining strength can be expected. The proportion of the thermoplastic resin on the surface of the joining surface is preferably 5 area% or more, more preferably 10 area% or more, and even more preferably 20 area% or more.

[0036] Furthermore, in the fiber-reinforced plastic of the present invention, a portion of the discontinuous reinforcing fiber bundles is in contact with both the thermosetting resin and the thermoplastic resin. By forming such a structure, when the joining surface of the fiber-reinforced plastic of the present invention is used to join the same or different materials and a load is applied, the strong reinforcing fibers in the discontinuous reinforcing fiber bundles that straddle the interface between the thermosetting resin and the thermoplastic resin bear the load. Therefore, the load applied to the interface between the thermosetting resin and the thermoplastic resin is reduced, suppressing peeling, and improving the apparent interfacial strength between the thermosetting resin and the thermoplastic resin.

[0037] Furthermore, since the reinforcing fibers are in contact with both the thermosetting resin and the thermoplastic resin, the interface shape between the thermosetting resin and the thermoplastic resin becomes complex. This increases the contact area between the thermosetting resin and the thermoplastic resin, and causes snagging due to unevenness, which is expected to further improve the apparent interface strength.

[0038] In the fiber-reinforced plastic of the present invention, the contact surface between the thermosetting resin and the thermoplastic resin may have any form, such as forming a mixed layer, but a more preferred form is one in which a region mainly composed of thermosetting resin 5 and a region mainly composed of thermoplastic resin 4 form interface 6 in the surface layer, as shown in Fig. 2. By adopting such an interface structure, it is possible to easily confirm the formation of a region in the fiber-reinforced plastic of the present invention in which the thermoplastic resin, which will be described later, is continuous from the surface in the thickness direction.

[0039] In the surface layer of the fiber-reinforced plastic of the present invention, it is preferable that a thermoplastic resin is present between the discontinuous reinforcing fiber bundles. By adopting such a configuration, a structure in which the interface shape between the thermosetting resin and the thermoplastic resin is complicated can be obtained, and improved bonding strength is expected. For example, such a structure can be confirmed by cutting out a cross section parallel to the thickness direction based on the longitudinal direction of a certain discontinuous reinforcing fiber bundle in the surface layer and observing it.

[0040] Here, the presence of thermoplastic resin between discontinuous reinforcing fiber bundles will be explained using the cross section of Figure 2 as an example. In a cross section cut in the thickness direction of fiber-reinforced plastic 1, a straight line is drawn from the longitudinal end of one discontinuous reinforcing fiber bundle 2 to the longitudinal end or side of another discontinuous reinforcing fiber bundle 2, without passing through the reinforcing fibers, so as to form the shortest distance between the fiber bundles. In this case, the line passes through the thermoplastic resin 4, thermosetting resin 5, and voids present between the fiber bundles, and the fact that the total length of the line passing through the thermoplastic resin 4 is 30% or more of the total length of the line indicates the presence of thermoplastic resin 4 between the discontinuous reinforcing fiber bundles 2.

[0041] Of the straight lines drawn between discontinuous reinforcing fiber bundles, the total length of which passes through the thermoplastic resin is 30% or more, and the proportion of the number of straight lines whose total length of which passes through the thermoplastic resin is 50% or more is preferably 30% or more, more preferably 50% or more, and even more preferably 80% or more.

[0042] In the fiber-reinforced plastic of the present invention, it is preferable that the thermoplastic resin occupies the spaces between any adjacent discontinuous reinforcing fiber bundles. With this configuration, the thermoplastic resin is sufficiently impregnated between the discontinuous reinforcing fiber bundles, resulting in a more complex structure of the interface between the thermosetting resin and the thermoplastic resin, which is expected to improve the bonding strength.

[0043] Here, "the thermoplastic resin occupies the space between any adjacent discontinuous reinforcing fiber bundles" means that it is possible to draw a line between the discontinuous reinforcing fiber bundles such that the total length of the line passing through the thermoplastic resin 4 is 100%. It is more preferable that it is possible to draw a line between a plurality of discontinuous reinforcing fiber bundles such that the total length of the line passing through the thermoplastic resin 4 is 100%.

[0044] In the fiber-reinforced plastic of the present invention, the volume content of the reinforcing fibers in the surface layer is preferably 15% by volume or more and 70% by volume or less. When the volume content is 15% by volume or more, the amount of thermosetting resin and thermoplastic resin is not too large compared to discontinuous reinforcing fiber bundles, and the specific strength and specific modulus tend to be excellent. Furthermore, when the volume content is 70% by volume or less, impregnation failure of the thermosetting resin and thermoplastic resin is unlikely to occur, and the resulting fiber-reinforced plastic tends to have fewer voids. The volume content is more preferably 20% by volume or more and 70% by volume or less, and even more preferably 25% by volume or more and 70% by volume or less.

[0045] Here, the volume content of reinforcing fibers in the surface layer means the volume content in the region where reinforcing fibers are present, and is measured and calculated excluding regions on the surface or between layers of the fiber-reinforced plastic that do not contain reinforcing fibers, or where the number of reinforcing fibers is small and resin accounts for the majority. Measurements are carried out at multiple locations, preferably five or more locations, and the volume content of reinforcing fibers is calculated at each location, and the average value is taken as the volume content of reinforcing fibers in the surface layer.

[0046] In the fiber-reinforced plastic of the present invention, the surface layer has a region in which the thermoplastic resin is continuous from the surface in the thickness direction, and the thickness of the portion in this region where the thermoplastic resin comes into contact with the discontinuous reinforcing fiber bundles is preferably at most 10 μm, more preferably at least 20 μm, and even more preferably at least 50 μm, from the viewpoints of making it easier for the discontinuous reinforcing fiber bundles to come into contact with the thermoplastic resin, making it easier for the reinforcing fibers to bear the load acting on the joining surface during joining, and further improving the joining strength (hereinafter, this thickness may be referred to as the "maximum impregnation distance").

[0047] Here, the region in which the thermoplastic resin is continuous from the surface in the thickness direction means that there is a region in which the boundary of the thermoplastic resin is continuous within the fiber-reinforced plastic when a cross section in the thickness direction is observed, as shown in Figure 4. This does not include regions that are not continuous from the thermoplastic resin 4, where the boundary is exposed when a cross section in the thickness direction is observed, such as thermoplastic resin 4' shown in Figure 5.

[0048] As shown in Figure 4, the maximum impregnation distance refers to the distance from the reference line 11, which is a line drawn parallel to the joining surface starting from the point where the thermoplastic resin, which is continuous in the thickness direction, first comes into contact with the reinforcing fiber bundle in the thickness direction, and is perpendicular to the reference line 11, to the intersection of the boundary line where the region where the thermoplastic resin, which is continuous from the surface in the thickness direction, comes into contact with other components (thermosetting resin, reinforcing fiber, or void) (measurement point 13, indicated by a black dot on perpendicular base line 12 in Figure 4).

[0049] In the present invention, the roughness average height Rc of the cross-sectional curve described below, as defined in JIS B0601 (2001), is preferably 3.5 μm or more, more preferably 10 μm or more, in a cross section in any direction when discontinuous reinforcing fiber bundles are stacked randomly, or in a cross section at an angle of 45 degrees to the arranging direction of the discontinuous reinforcing fiber bundles when the discontinuous reinforcing fiber bundles are arranged in one direction. Such a structure is thought to be formed by the flow of the discontinuous reinforcing fiber bundles and the thermosetting resin / thermoplastic resin.

[0050] By setting the roughness average height Rc to 3.5 μm or more, the contact area between the thermoplastic resin and the thermosetting resin increases, and the unevenness creates complex catching, which is expected to further improve the apparent interfacial strength. In addition, the discontinuous reinforcing fibers present at the interface chemically and / or physically bond with the thermosetting resin and the thermoplastic resin, improving the interfacial strength between the thermosetting resin and the thermoplastic resin.

[0051] The roughness average height Rc can be measured by any known method, such as a method of measuring from a cross-sectional image of a fiber-reinforced plastic obtained using X-ray CT, a method of measuring from an elemental analysis mapping image obtained using an energy dispersive X-ray spectrometer (EDS), or a method of measuring from a cross-sectional observation image obtained using an optical microscope, a scanning electron microscope (SEM), or a transmission electron microscope (TEM).

[0052] In observing the image, the thermosetting resin and / or thermoplastic resin may be dyed to adjust the contrast. In the image obtained by any of the above methods, the roughness average height Rc of the cross-sectional curve is measured within an area of ​​500 μm square.

[0053] An example of a method for measuring the roughness average height Rc is shown in Figures 6 and 7. Figure 6 is a schematic cross-sectional view of a fiber-reinforced plastic of the present invention. In Figure 6, the roughness average height Rc is measured in a region of the interface 6 where the thermosetting resin 5 and the thermoplastic resin 4 are in contact, which has discontinuous reinforcing fiber bundles 2 containing discontinuous reinforcing fibers 3 that are in contact with both the thermosetting resin 5 and the thermoplastic resin 4.

[0054] Figure 7 is an enlarged view of the area in Figure 6 used to measure the surface roughness average height Rc. In Figure 7, thermosetting resin 5 contacts thermoplastic resin 4 at interface 6. Also, multiple discontinuous reinforcing fibers 3 contained in a discontinuous reinforcing fiber bundle are present on interface 6. Vertical base lines 12 are drawn at 5 μm intervals from base line 11 through thermoplastic resin 4 toward thermosetting resin 5. Measurement points 14 where vertical base line 12 drawn from base line 11 first intersects with thermosetting resin 5 are plotted, and the line connecting the plotted points is defined as a cross-sectional curve. The resulting cross-sectional curve is subjected to filtering based on JIS B0601 (2001) to calculate the surface roughness average height Rc of the cross-sectional curve.

[0055] The basis weight of the thermoplastic resin used in the surface layer of the fiber reinforced plastic of the present invention is preferably 10 g / m 2 More preferably, it is 20 g / m or more. 2 The weight of the thermoplastic resin is 10 g / m 2 If the thickness is equal to or greater than this, a sufficient thickness for achieving excellent bonding strength can be obtained.

[0056] The upper limit of the weight of the thermoplastic resin in the surface layer is not particularly limited, but since the content of the thermoplastic resin is not too large compared to the content of the reinforcing fiber and a fiber-reinforced plastic excellent in specific strength and specific modulus is obtained, it is preferable that the upper limit be 500 g / m 2Here, the basis weight of the thermoplastic resin is the weight of the surface layer of the fiber reinforced plastic per 1 m 2 This refers to the mass (g) of thermoplastic resin contained per unit.

[0057] The amount of reinforcing fibers per unit area in the surface layer of the fiber-reinforced plastic of the present invention is 30 g / m 2 More than 2,000g / m 2 The amount of reinforcing fibers is preferably 30 g / m or less. 2 When the amount of reinforcing fibers is 2,000 g / m or more, the number of substrates required to obtain a predetermined thickness during fiber-reinforced plastic molding can be reduced, which makes the process easier. 2 If it is equal to or less than this, the drapeability as a precursor of fiber reinforced plastic is likely to be improved.

[0058] In addition, in the surface layer of the fiber-reinforced plastic of the present invention, the ratio of voids in contact with the longitudinal ends of the discontinuous reinforcing fiber bundles is preferably 5% by area or less. By adopting such a configuration, stress concentration at the longitudinal ends of the discontinuous reinforcing fiber bundles can be prevented, and a fiber-reinforced plastic with excellent molding quality and strength can be obtained.

[0059] The presence ratio of voids in contact with the longitudinal ends of discontinuous reinforcing fiber bundles is measured as follows. First, when the discontinuous reinforcing fiber bundles are stacked randomly, a cross-sectional image in any direction is obtained. When the discontinuous reinforcing fiber bundles are arranged in one direction, a plurality of cross-sectional images in the thickness direction, which is a direction parallel to the arrangement direction, are obtained. Next, in each of the obtained images, the area of ​​the voids in contact with the longitudinal ends of the discontinuous reinforcing fiber bundles and the area of ​​the portion corresponding to the surface layer are measured. Finally, in all images, the total area of ​​the measured voids is divided by the total area of ​​the portion corresponding to the surface layer, and the result is multiplied by 100 to obtain the presence ratio (%) of voids in contact with the longitudinal ends of the discontinuous reinforcing fiber bundles. The presence ratio of voids in contact with the longitudinal ends of the discontinuous reinforcing fiber bundles is more preferably 3 area % or less, and even more preferably 1 area % or less.

[0060] The cross-sectional image of the fiber-reinforced plastic can be obtained by cutting the plastic in the thickness direction at an arbitrary location, embedding and polishing the cut plastic, and then observing the cut plastic using an optical microscope.

[0061] Furthermore, in the surface layer of the fiber-reinforced plastic of the present invention, it is preferable that the reinforcing fibers and the thermoplastic resin are in continuous contact from the longitudinal end of the reinforcing fibers in the longitudinal direction of the fibers (hereinafter, the length of this contact portion may be referred to as the "longitudinal impregnation distance"). With such a configuration, a structure can be obtained in which the interface shape between the thermosetting resin and the thermoplastic resin through the reinforcing fibers is more complex, and improved bonding strength is expected. It is believed that such a structure is formed by the flow of discontinuous reinforcing fiber bundles and the thermosetting resin and thermoplastic resin.

[0062] The length of continuous contact between the reinforcing fiber and the thermoplastic resin from the longitudinal end of the reinforcing fiber in the longitudinal direction of the fiber refers to the distance, as shown in Figure 8, from the end of any discontinuous reinforcing fiber 3 that is in contact with the thermoplastic resin at its longitudinal end as the starting point, to the intersection of a line drawn along the side of the reinforcing fiber as a reference line 15 and the boundary line where the thermoplastic resin 4 first comes into contact with the thermosetting resin 5 or a void (measurement point 16 indicated by a black dot on reference line 15 in Figure 8).

[0063] More specifically, the longitudinal impregnation distance is measured as follows. First, five or more discontinuous reinforcing fiber bundles located near the surface are randomly selected, and cross-sectional images in the thickness direction are obtained for each of the discontinuous reinforcing fiber bundles, parallel to the orientation direction of the reinforcing fibers constituting the discontinuous reinforcing fiber bundles. Next, for each of the obtained images, a reference line is drawn along the longitudinal direction of the reinforcing fiber from the longitudinal end where the reinforcing fiber contacts both the thermosetting resin and the thermoplastic resin. The point where this line first intersects with the thermosetting resin or a void is extracted, and the distance from the end is measured. The average of all measured values ​​is taken as the longitudinal impregnation distance. Note that when measuring the longitudinal impregnation distance, when the fiber-reinforced plastic is cut parallel to the thickness direction, the side of the reinforcing fiber closest in the thickness direction to the surface where the thermoplastic resin is exposed in the surface layer is excluded from the measurement object.

[0064] In the fiber-reinforced plastic of the present invention, the longitudinal impregnation distance is preferably 20 μm or more, more preferably 50 μm or more, and even more preferably 100 μm or more, from the viewpoint of making it easier for the reinforcing fibers to bear the load acting on the joining surface and further improving the joining strength.

[0065] The fiber-reinforced plastic of the present invention may consist of only the surface layer, but may also have a layer structure including layers other than the surface layer. By having such a layer structure, the thickness of the fiber-reinforced plastic of the present invention can be increased, allowing the fiber-reinforced plastic of the present invention to be used in structural components. The layers other than the surface layer may be layers consisting of continuous or discontinuous reinforcing fibers and a matrix composed of a thermosetting resin and / or a thermoplastic resin. There are no particular restrictions on the types of layers that make up such a layer structure.

[0066] Furthermore, in the fiber reinforced plastic of the present invention, a resin layer containing no reinforcing fibers and made of a thermosetting resin and / or a thermoplastic resin may be present.

[0067] In the fiber-reinforced plastic of the present invention, another component (hereinafter sometimes referred to as the "adherend") can be joined to the thermoplastic resin present at the joining surface of the fiber-reinforced plastic by some kind of heating means, and integrated (welded) with the fiber-reinforced plastic through the thermoplastic resin.

[0068] Examples of the adherend include a member containing a thermosetting resin and / or a thermoplastic resin, and a member containing a metal. A member made of the fiber-reinforced plastic of the present invention can also be used as the adherend. The method for integrating the fiber-reinforced plastic of the present invention with the adherend is not particularly limited, and examples include heat welding, vibration welding, ultrasonic welding, laser welding, resistance welding, induction welding, insert injection molding, and outsert injection molding.

[0069] Examples of the thermosetting resin contained in the matrix of the fiber-reinforced plastic of the present invention include unsaturated polyester resins, vinyl ester resins, epoxy resins, phenolic resins, urea resins, melamine resins, thermosetting polyimide resins, cyanate ester resins, bismaleimide resins, benzoxazine resins, copolymers thereof, modified products thereof, and resins obtained by blending at least two of these. To improve impact resistance, an elastomer or rubber component may be added to the thermosetting resin. Furthermore, the fiber-reinforced plastic of the present invention may contain a curing agent or curing accelerator to control curing.

[0070] Among these, from the viewpoint of practicality and versatility, epoxy resins, phenolic resins, unsaturated polyester resins, vinyl ester resins, thermosetting polyimide resins, cyanate ester resins, bismaleimide resins, and benzoxazine resins are preferred, and epoxy resins are more preferred.

[0071] Epoxy resins are preferred because they have excellent mechanical properties, heat resistance, and adhesion to reinforcing fibers. Examples of the main component of the epoxy resin include bisphenol-type epoxy resins such as bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, bisphenol AD-type epoxy resins, and bisphenol S-type epoxy resins, brominated epoxy resins such as tetrabromobisphenol A diglycidyl ether, epoxy resins having a biphenyl skeleton, epoxy resins having a naphthalene skeleton, epoxy resins having a dicyclopentadiene skeleton, novolac-type epoxy resins such as phenol novolac-type epoxy resins and cresol novolac-type epoxy resins, and N,N,O-triglycidyl-m-aminophenol. Examples of the epoxy resins include glycidyl amine epoxy resins such as phenol, N,N,O-triglycidyl-p-aminophenol, N,N,O-triglycidyl-4-amino-3-methylphenol, N,N,N',N'-tetraglycidyl-4,4'-methylenedianiline, N,N,N',N'-tetraglycidyl-2,2'-diethyl-4,4'-methylenedianiline, N,N,N',N'-tetraglycidyl-m-xylylenediamine, N,N-diglycidylaniline, and N,N-diglycidyl-o-toluidine; resorcinol diglycidyl ether; and triglycidyl isocyanurate.

[0072] Examples of the thermoplastic resin contained in the matrix of the fiber-reinforced plastic of the present invention include polyester-based resins such as polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, and liquid crystal polyester, polyolefins such as polyethylene, polypropylene, and polybutylene, polyamides such as polyamide 6 and polyamide 66, polyarylene ether ketones such as polyketone, polyether ketone, polyether ether ketone, and polyether ketone ketone, styrene-based resins, urethane resins, polyoxymethylene, polycarbonate, polymethyl methacrylate, polyvinyl chloride, polyphenylene sulfide, polyphenylene ether, modified polyphenylene ether, polyimide, polyamideimide, polyetherimide, polysulfone, modified polysulfone, polyethersulfone, polyarylate, polyethernitrile, phenolic resins, and phenoxy resins. These thermoplastic resins may also be copolymers or modified products of the above-mentioned resins, and / or resins in which two or more types are blended.

[0073] Among these, from the viewpoint of heat resistance, it is preferable that one or more selected from polyarylene ether ketone, polyphenylene sulfide, and polyetherimide are contained in the thermoplastic resin in an amount of 60 mass% or more. To improve impact resistance, an elastomer or rubber component may be added to the thermoplastic resin.

[0074] Furthermore, depending on the application, etc., the thermosetting resin and the thermoplastic resin may contain other fillers or additives as appropriate, as long as the object of the present invention is not impaired. The thermosetting resin and the thermoplastic resin may contain, for example, an inorganic filler, a flame retardant, a conductivity imparting agent, a crystal nucleating agent, an ultraviolet absorber, an antioxidant, a vibration damping agent, an antibacterial agent, an insect repellent, a deodorizing agent, a coloring inhibitor, a heat stabilizer, a release agent, an antistatic agent, a plasticizer, a lubricant, a colorant, a pigment, a dye, a foaming agent, a foam control agent, a coupling agent, etc.

[0075] The fiber-reinforced plastic of the present invention is not particularly limited in its application, but is preferably used for aircraft structural members, wind turbine blades, automobile outer panels, computer applications such as IC trays and notebook computer housings, and sports applications such as golf shafts and tennis rackets.

[0076] [Method of manufacturing fiber-reinforced plastics] The method for producing a fiber-reinforced plastic of the present invention comprises: Step 1: impregnating a reinforcing fiber bundle with a thermosetting resin; Step 2: impregnating the reinforcing fiber bundle with a thermoplastic resin; Step 3: cutting the reinforcing fiber bundles to form discontinuous reinforcing fiber bundles; A step 4 of laminating a required number of substrates constituting a fiber reinforced plastic so that the thermoplastic resin is exposed on at least one surface in the thickness direction; and step 5 of molding the fiber reinforced plastic by heating and pressurizing, The step 5 is carried out after the steps 1 to 4 have been carried out, or after the steps 1, 3 and 4 have been carried out and simultaneously with the step 2, or after the steps 2, 3 and 4 have been carried out and simultaneously with the step 1.

[0077] In the method for producing a fiber-reinforced plastic of the present invention, the viscosity of the thermosetting resin and the thermoplastic resin is reduced by heating. By applying pressure in this state, the discontinuous reinforcing fiber bundles flow together with the thermosetting resin and the thermoplastic resin by shaping and / or stretching, and a fiber-reinforced plastic can be molded in which the discontinuous reinforcing fiber bundles are sufficiently impregnated with the thermosetting resin and the thermoplastic resin while conforming to a complex shape.

[0078] When step 5 is performed after steps 1 to 4, steps 1 to 4 may be performed in any order, and the order of performing steps is not limited. For example, as long as the thermoplastic resin is exposed on at least one surface layer in the thickness direction, impregnation with a thermosetting resin or a thermoplastic resin, cutting of the reinforcing fiber bundles, etc. may be performed after laminating the substrates that constitute the fiber-reinforced plastic. Thereafter, the fiber-reinforced plastic of the present invention is molded by step 5.

[0079] Furthermore, when step 5 is carried out simultaneously with step 2, the two steps can be carried out simultaneously, making it possible to efficiently produce the fiber-reinforced plastic of the present invention. In this case, steps 1, 3, and 4 may be carried out in any order, and there are no restrictions on the order of their implementation, as long as the thermoplastic resin is exposed to at least one surface layer in the thickness direction. Thereafter, by carrying out step 5 and step 2 simultaneously, the thermoplastic resin is impregnated into the discontinuous reinforcing fiber bundles, and the fiber-reinforced plastic of the present invention is molded.

[0080] Similarly, when step 5 is carried out simultaneously with step 1, the two steps can be carried out simultaneously, making it possible to efficiently produce the fiber-reinforced plastic of the present invention. In this case, steps 2, 3, and 4 may be carried out in any order, and there are no restrictions on the order in which they are carried out, as long as the thermoplastic resin is exposed to at least one surface layer in the thickness direction. Thereafter, by carrying out step 5 and step 1 simultaneously, the fiber-reinforced plastic of the present invention is molded while the thermosetting resin is impregnated into the discontinuous reinforcing fiber bundles.

[0081] In step 1, the method for impregnating the reinforcing fiber bundles with the thermosetting resin is not particularly limited, and examples thereof include a method in which a discontinuous reinforcing fiber bundle obtained by cutting a reinforcing fiber bundle into a predetermined shape is impregnated with the thermosetting resin; a method in which an intermediate containing a thermoplastic resin and discontinuous reinforcing fiber bundles is impregnated with the thermosetting resin; a method in which a unidirectional prepreg impregnated with a thermoplastic resin is cut to a certain width and fiber length using a roll cutter or the like, and then dispersed into a sheet and impregnated from one or both sides with the thermosetting resin; and a method in which a cut is made at a specific location of the unidirectional prepreg using a rotary blade, Thomson blade, automatic cutting machine, laser irradiation, or the like, and then the thermosetting resin is impregnated from one or both sides.

[0082] In step 2, the method for impregnating the reinforcing fiber bundles with the thermoplastic resin is not particularly limited. Examples of the method include a method in which a discontinuous reinforcing fiber bundle obtained by cutting a reinforcing fiber bundle into a predetermined shape is impregnated with the thermoplastic resin; a method in which an intermediate containing a thermosetting resin and discontinuous reinforcing fiber bundles is impregnated with the thermoplastic resin; a method in which a unidirectional prepreg impregnated with a thermosetting resin is cut to a certain width and fiber length using a roll cutter or the like, and then dispersed into a sheet and impregnated from one or both sides with the thermoplastic resin; and a method in which a cut is made at a specific location of the unidirectional prepreg using a rotary blade, Thomson blade, automatic cutting machine, laser irradiation, or the like, and then the thermoplastic resin is impregnated from one or both sides.

[0083] In step 3, the method for cutting the reinforcing fiber bundles to form discontinuous reinforcing fiber bundles is not particularly limited, and examples thereof include a method of cutting a unidirectional prepreg impregnated with a thermosetting resin and / or a thermoplastic resin to a certain width and fiber length using a roll cutter or the like, and a method of inserting incisions into specific locations of the unidirectional prepreg using a rotary blade, a Thomson blade, an automatic cutting machine, laser irradiation, or the like.

[0084] In step 4, there are no particular limitations on the method for stacking the required number of substrates that make up the fiber-reinforced plastic so that the thermoplastic resin is exposed on at least one surface in the thickness direction, and examples include a method of stacking by hand or a method of stacking using a robot arm, etc.

[0085] In step 5, the heating temperature and pressure vary depending on the types of thermosetting resin and thermoplastic resin used in the fiber-reinforced plastic of the present invention. The heating temperature and pressure may be within a range of temperature and pressure at which both the thermosetting resin and the thermoplastic resin flow, and, if necessary, may be within a range of temperature and pressure at which the discontinuous reinforcing fiber bundles flow together with both resins.

[0086] Examples of the method of heating and pressing include a heating and pressing method using a heat roll, a press molding method, an autoclave molding method, a vacuum pressure molding method, and an internal pressure molding method.

[0087] Furthermore, it is preferable that the method for producing a fiber-reinforced plastic of the present invention further includes step 6 of flowing the substrate so that the longitudinal ends of the discontinuous reinforcing fiber bundles come into contact with the thermosetting resin or thermoplastic resin in the surface layer where the thermoplastic resin is exposed.

[0088] By bringing the longitudinal ends of the discontinuous reinforcing fiber bundles into contact with the thermosetting resin or thermoplastic resin, stress concentration at the longitudinal ends of the discontinuous reinforcing fiber bundles can be prevented, and the characteristics of the fiber-reinforced plastic of the present invention can be further expressed, which is preferable.

[0089] Step 6 is preferably carried out before or simultaneously with step 5.

[0090] In step 6, it is preferable to flow the substrate so that in the surface layer where the thermoplastic resin is exposed, at least a portion of the discontinuous reinforcing fiber bundles is in contact with both the thermosetting resin and the thermoplastic resin, and at least one of the reinforcing fibers constituting the reinforcing fiber bundle is in continuous contact with the thermoplastic resin in the longitudinal direction from the longitudinal end of the reinforcing fiber.

[0091] By having the thermoplastic resin continuously contact the reinforcing fibers from their longitudinal ends in the longitudinal direction, the shape of the interface between the thermosetting resin and the thermoplastic resin through the reinforcing fibers becomes more complex, and the bond between the thermosetting resin and the thermoplastic resin becomes stronger, which is preferable as it allows the characteristics of the fiber-reinforced plastic of the present invention to be further expressed.

[0092] Furthermore, in step 6, it is preferable to flow the base material so that there is a combination in which only the thermoplastic resin is present at the longitudinal end of a discontinuous reinforcing fiber bundle and on a line connecting a different discontinuous reinforcing fiber bundle.

[0093] By having a combination in which only the thermoplastic resin is present at the longitudinal end of a discontinuous reinforcing fiber bundle and on the line connecting different discontinuous reinforcing fiber bundles, a structure in which the thermoplastic resin deeply impregnates the fiber bundles can be easily achieved. As a result, a more complex structure can be achieved at the interface between the thermosetting resin and the thermoplastic resin, and the bond between the thermosetting resin and the thermoplastic resin can be stronger, which is preferable as it further exhibits the characteristics of the fiber-reinforced plastic of the present invention.

[0094] The fiber-reinforced plastic of the present invention can be produced by laminating the substrate constituting the fiber-reinforced plastic alone or together with other prepregs, sheet molding compounds, cut prepregs, etc. by a known method, and then heating and pressurizing the resulting laminate to cure it.

[0095] In this case, it is sufficient that the thermoplastic resin is exposed on at least one surface layer in the thickness direction of the produced fiber reinforced plastic, and there are no restrictions on the order of lamination of the other layers.

[0096] The fiber-reinforced plastic of the present invention may also be produced by stretch-molding a substrate constituting the fiber-reinforced plastic by press molding. The fiber-reinforced plastic of the present invention contains discontinuous reinforcing fiber bundles. Therefore, when press molding is used, the discontinuous reinforcing fiber bundles also flow as the thermosetting resin and thermoplastic resin contained in the fiber-reinforced plastic flow, and the fiber-reinforced plastic of the present invention has excellent shape conformability. Examples of structures with excellent shape conformability include, but are not limited to, structures in which the discontinuous reinforcing fiber bundles are oriented in the out-of-plane direction, such as ribbed shapes and uneven shapes.

[0097] In this case, the shape formed by stretch molding is not particularly limited as long as the substrate can sufficiently conform to the shape and sufficient surface quality and bonding strength can be maintained, but it is preferable to mold the surface area of ​​the surface layer to be 100% to 200% of the surface area of ​​the substrate that constitutes the fiber-reinforced plastic, in order to express the excellent shape-following properties of the fiber-reinforced plastic of the present invention. The range of the surface area of ​​the molded product relative to the surface area of ​​the substrate is preferably 100% to 180%, more preferably 100% to 150%. [Example]

[0098] 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. Measurements of various properties were carried out in an environment of 23°C and 50% relative humidity unless otherwise noted.

[0099] <Material> The following materials were used:

[0100] Reinforced fiber [A] Carbon fiber ("Torayca (registered trademark)" T700S-24K, manufactured by Toray Industries, Inc., strand tensile strength: 4.9 GPa) was used.

[0101] ·Thermosetting resin [B] Epoxy resin base materials ["jER" (registered trademark) 828 (Mitsubishi Chemical Corporation)], ["jER" (registered trademark) 1001 (Mitsubishi Chemical Corporation)], and ["jER" (registered trademark) 154 (Mitsubishi Chemical Corporation)] were added in amounts of 30 parts by mass, 40 parts by mass, and 30 parts by mass, respectively, and the mixture was heated and kneaded at 150°C until the components were compatible. Next, while continuing to knead, the mixture was cooled to 80°C, and then 26 parts by mass of a curing agent [3,3'DAS (3,3'-diaminodiphenyl sulfone, Mitsubishi Fine Chemical Corporation)] was added and kneaded for 30 minutes at 80°C, yielding thermosetting resin [B].

[0102] ·Thermoplastic resin [C] A sheet of polyamide 6 ("Amilan" (registered trademark) CM4000 (manufactured by Toray Industries, Inc., terpolymer polyamide resin, melting point 155°C)) was used.

[0103] <Evaluation method> Maximum impregnation distance and average roughness height The cross sections of the fiber-reinforced plastics produced in each example and comparative example were embedded and polished, and then observed using an optical microscope in a 500 μm square area near the bonding surface. Carbon fiber, thermoplastic resin, and thermosetting resin were distinguished from each other based on the contrast of the images obtained.

[0104] Next, in the region where the thermoplastic resin continues from the joint surface in the thickness direction, the point where it first contacts the reinforcing fiber was extracted, and a line drawn parallel to the joint surface from that point was used as the reference line. Vertical base lines were drawn at 5 μm intervals from the reference line through the thermoplastic resin toward the thermosetting resin, and all points where the vertical base lines first intersected with the thermosetting resin, reinforcing fiber, or voids were plotted. The maximum distance from the plotted points to the reference line was used as the maximum impregnation distance.

[0105] Furthermore, in Examples 1-1 to 1-4 and Comparative Examples 1-1 and 1-2 described below, a surface was cut out at an angle of 45 degrees to an arbitrary direction, and in Examples 2-1, 2-2 and Comparative Example 2-1, a surface at an angle of 45 degrees to the orientation direction of the reinforcing fibers at the bonding surface was cut out, and after embedding and polishing the cross section, a 500 μm square area near the bonding surface was observed using an optical microscope. Then, a reference line and a vertical base line were created in the same manner as in the measurement of the maximum impregnation distance, and the measurement point where the vertical base line first intersected with the thermosetting resin was plotted. The line connecting the plotted points was taken as the cross-sectional curve, and filtering processing was performed to calculate the roughness average height.

[0106] Longitudinal impregnation distance Discontinuous reinforcing fiber bundles located near the surface were randomly selected, and the fiber-reinforced plastic was cut parallel to the thickness direction so that the cut was parallel to the orientation direction of the reinforcing fibers constituting the discontinuous reinforcing fiber bundle. Multiple locations were extracted where the thermoplastic resin, which continued from the joint surface in the thickness direction, contacted the longitudinal ends of the reinforcing fibers constituting the discontinuous reinforcing fiber bundle. For the reinforcing fibers in the discontinuous reinforcing fiber bundle that were in contact with both the thermosetting resin and the thermoplastic resin, a reference line was drawn along the longitudinal direction of the reinforcing fiber from the longitudinal end where the reinforcing fiber contacted the thermoplastic resin. The point where this first intersected with the thermosetting resin or void was extracted, and the average value was taken as the longitudinal impregnation distance.

[0107] Measurement of the length of passage through thermoplastic resin between discontinuous reinforcing fiber bundles In the image used to measure the longitudinal impregnation distance, a straight line was drawn from the longitudinal end of the discontinuous reinforcing fiber bundle to the end or side of another discontinuous reinforcing fiber bundle that was the shortest distance, without passing through the reinforcing fibers, and the total length passing through the thermoplastic resin was measured. Of these, the straight lines whose total length passing through the thermoplastic resin was 30% or more were selected, and the percentage of the number of straight lines whose total length passing through the thermoplastic resin was 50% or more was evaluated based on the following criteria.

[0108] A: 80% or more B: 50% or more but less than 80% C: 30% or more but less than 50% D: There are no straight lines whose total length passes through the thermoplastic resin less than 30% or 30% or more

[0109] - Volume content of reinforcing fibers In Examples 1-1 to 1-4 and Comparative Examples 1-1 and 1-2, fiber-reinforced plastics were cut in an arbitrary direction, embedded, and polished, and then cross-sectional images of discontinuous reinforcing fiber bundles in the surface layer were obtained using an optical microscope. From the cross-sectional images, discontinuous reinforcing fiber bundles oriented approximately perpendicular to the observation surface were selected, and the fiber volume content of the discontinuous reinforcing fiber bundles was calculated from the area ratio. The fiber volume contents were calculated for multiple discontinuous reinforcing fiber bundles, and the average value was used as the volume content of the reinforcing fibers in the surface layer.

[0110] In addition, in Examples 2-1 and 2-2 and Comparative Example 2-1, the fiber-reinforced plastic was cut in a direction perpendicular to the orientation direction of the reinforcing fibers in the surface layer, embedded, and polished, and then a cross-sectional image of the discontinuous reinforcing fiber bundles in the surface layer was obtained using an optical microscope. Next, the fiber volume content of the discontinuous reinforcing fibers in the cross-sectional image was calculated from the area ratio. The fiber volume content was calculated at multiple locations, and the average value was used as the volume content of the reinforcing fibers in the surface layer.

[0111] Tensile shear bond strength The fiber-reinforced plastics produced in each Example and Comparative Example were cut into two pieces measuring 250 mm in width and 92.5 mm in length, and dried in a vacuum oven for 24 hours. The two fiber-reinforced plastics were then placed one on top of the other, with the sides having the thermoplastic resin [C] facing each other. The total area of ​​the overlap was 250 mm in width and 12.5 mm in length.

[0112] The overlapping surfaces were then welded together under a pressure of 3 MPa at a temperature 20°C higher than the melting point of the thermoplastic resin [C] and held for 1 minute to obtain an integrated molded product. A tab was attached to the obtained integrated molded product in accordance with ISO4587:1995 (JIS K6850(1994)), and the product was cut to a width of 25 mm to obtain a test specimen.

[0113] The obtained test pieces were dried in a vacuum oven for 24 hours, and the tensile shear bond strength was measured in accordance with ISO4587:1995 (JIS K6850 (1994)). The measurement results were evaluated according to the following criteria.

[0114] A:30MPa or more B: 10 MPa or more and less than 30 MPa C: Less than 10 MPa (failed) or not bonded

[0115] <Example 1-1> Reinforced fiber sheet (weight 120g / m) in which reinforcing fibers [A] are oriented in one direction 2) was drawn out to produce a continuous reinforcing fiber bundle. After a thin layer of thermosetting resin [B] was applied to the obtained continuous reinforcing fiber bundle, it was continuously inserted into a rotary cutter with blades provided at 25 mm intervals in the circumferential direction to produce a chopped fiber bundle (discontinuous reinforcing fiber bundle).

[0116] In addition, thermosetting resin [B] was applied onto the release film to prepare two sheets of thermosetting resin [B].

[0117] The chopped fiber bundles were then uniformly scattered on one sheet of the thermosetting resin [B], and another sheet of the thermosetting resin [B] was placed on top of it. The two sheets were heated at 100°C to prevent the thermosetting resin [B] from curing, and pressed together using a roller at 0.07 MPa to produce an SMC prepreg. The volume content of the reinforcing fiber [A] in the SMC prepreg was adjusted to 40%. The scattered chopped fiber bundles were stacked in the SMC prepreg.

[0118] Eight SMC prepregs cut into 300 mm squares were stacked together, and a thermoplastic resin [C] sheet was attached to one surface to obtain a fiber-reinforced plastic uncured laminate.

[0119] The above uncured fiber-reinforced plastic laminate was set in a mold with a surface area of ​​300 mm x 300 mm, and a pressure of 0.6 MPa was applied using a press to eliminate voids, and the laminate was heated at 180°C for 2 hours to obtain a fiber-reinforced plastic.

[0120] The obtained fiber-reinforced plastic had little unevenness in thickness. Furthermore, it was possible to confirm from cross-sectional observation that the region mainly composed of thermosetting resin [B] and the region mainly composed of thermoplastic resin [C] flowed together to form an interface, and that the thermoplastic resin [C] was impregnated between the discontinuous reinforcing fiber bundles. Furthermore, in all observed regions, the longitudinal ends of the discontinuous reinforcing fiber bundles were in contact with the thermosetting resin or thermoplastic resin within the visual range.

[0121] Some of the discontinuous reinforcing fiber bundles located on the surface layer were in contact with both the thermosetting resin and the thermoplastic resin, and at least some of the reinforcing fibers constituting the discontinuous reinforcing fiber bundles were in contact with both the thermosetting resin and the thermoplastic resin, and there were some in which the reinforcing fibers and the thermoplastic resin were in continuous contact from the longitudinal end of the reinforcing fiber in the longitudinal direction. Furthermore, a straight line could be drawn between multiple discontinuous reinforcing fiber bundles, with the total length passing through the thermoplastic resin being 100%. The obtained fiber-reinforced plastic exhibited sufficient bonding strength.

[0122] <Example 1-2> A fiber-reinforced plastic was obtained in the same manner as in Example 1-1, except that the fiber-reinforced plastic uncured laminate was set in a mold with a surface area of ​​350 mm x 350 mm and stretched by applying a pressure of 3 MPa using a press.

[0123] The obtained fiber-reinforced plastic was thinner than that of Example 1-1 but had little unevenness in thickness, and the fiber-reinforced plastic after pressing was stretched to a 350 mm square with no gaps, exhibiting excellent shape conformability. Furthermore, since the distance between the discontinuous reinforcing fiber bundles was wider than that of Example 1-1, the impregnation of the thermoplastic resin [C] between the discontinuous reinforcing fiber bundles was more clearly visible than in Example 1-1, and in all observed regions, the longitudinal ends of the discontinuous reinforcing fiber bundles were in contact with the thermosetting resin or thermoplastic resin within the visual range.

[0124] A portion of the discontinuous fiber-reinforced fiber bundles located in the surface layer was in contact with both the thermosetting resin and the thermoplastic resin, and at least a portion of the reinforcing fibers constituting the discontinuous fiber bundles were in contact with both the thermosetting resin and the thermoplastic resin, and there were some in which the reinforcing fibers and the thermoplastic resin were in continuous contact from the longitudinal end of the reinforcing fiber in the longitudinal direction. Furthermore, a straight line could be drawn between the multiple discontinuous fiber bundles, with the total length passing through the thermoplastic resin being 100%. The obtained fiber-reinforced plastic exhibited sufficient bonding strength.

[0125] <Examples 1-3> Eight sheets of SMC prepreg cut to a 300 mm square and eight sheets of thermoplastic resin [C] were prepared. One thermoplastic resin [C] sheet was placed on the underside of each SMC prepreg to obtain an uncured fiber-reinforced plastic laminate in which SMC prepregs and thermoplastic resin [C] sheets were alternately laminated. The uncured fiber-reinforced plastic laminate was cured and bonded using the method described in Example 1-1 to obtain a fiber-reinforced plastic with the thermoplastic resin [C] exposed on one surface.

[0126] The obtained fiber-reinforced plastic had little unevenness in thickness. Furthermore, it was possible to confirm from cross-sectional observation that the region mainly composed of thermosetting resin [B] and the region mainly composed of thermoplastic resin [C] had flowed to contact each other, forming an interface, and that the thermoplastic resin [C] had impregnated between the discontinuous reinforcing fiber bundles. Furthermore, in all observed regions, the longitudinal ends of the discontinuous reinforcing fiber bundles were in contact with the thermosetting resin or thermoplastic resin within the visual range.

[0127] Some of the discontinuous reinforcing fiber bundles located in the surface layer were in contact with both the thermosetting resin and the thermoplastic resin, and at least some of the reinforcing fibers constituting the discontinuous reinforcing fiber bundles were in contact with both the thermosetting resin and the thermoplastic resin. Furthermore, some of the reinforcing fibers and the thermoplastic resin were in continuous contact with each other from the longitudinal end of the reinforcing fiber in the longitudinal direction. Furthermore, a straight line could be drawn between multiple discontinuous reinforcing fiber bundles, with the total length passing through the thermoplastic resin being 100%. In layers other than the surface layer, layers composed of thermoplastic resin were observed between the layers. The fiber-reinforced plastic obtained exhibited sufficient bonding strength.

[0128] <Examples 1-4> A fiber-reinforced plastic was obtained in the same manner as in Example 1-3, except that the fiber-reinforced plastic uncured laminate was set in a mold with a surface area of ​​350 mm x 350 mm and stretched by applying a pressure of 3 MPa using a press.

[0129] The obtained fiber reinforced plastic was thinner than that of Example 1-3 but had little unevenness in thickness, and the fiber reinforced plastic after pressing was stretched to a 350 mm square with no gaps, exhibiting excellent shape conformability. Furthermore, since the distance between the discontinuous reinforcing fiber bundles was wider than that of Example 1-3, the impregnation of the thermoplastic resin [C] between the discontinuous reinforcing fiber bundles was more clearly visible than in Example 1-3, and in all observed regions, the longitudinal ends of the discontinuous reinforcing fiber bundles were in contact with the thermosetting resin or thermoplastic resin within the visual range.

[0130] Some of the discontinuous reinforcing fiber bundles located in the surface layer were in contact with both the thermosetting resin and the thermoplastic resin, and at least some of the reinforcing fibers constituting the discontinuous reinforcing fiber bundles were in contact with both the thermosetting resin and the thermoplastic resin. Furthermore, some of the reinforcing fibers and the thermoplastic resin were in continuous contact with each other from the longitudinal end of the reinforcing fiber in the longitudinal direction. Furthermore, a straight line could be drawn between multiple discontinuous reinforcing fiber bundles, with the total length passing through the thermoplastic resin being 100%. In layers other than the surface layer, layers composed of thermoplastic resin were observed between the layers. The fiber-reinforced plastic obtained exhibited sufficient bonding strength.

[0131] <Example 2-1> A continuous reinforced fiber sheet (120 g / m2) in which reinforced fibers [A] are aligned in one direction. 2 ) was pulled out and run in one direction. In addition, the thermosetting resin [B] was coated on a release film to produce two sheets of the thermosetting resin [B]. Then, the thermosetting resin [B] sheets were pressed from above and below the reinforcing fiber [A] sheet running in one direction using rollers at 0.07 MPa while being heated at a temperature of 100°C so as not to harden the thermosetting resin [B], thereby producing a unidirectional prepreg.

[0132] Then, using a rotary blade, incisions were made in the reinforcing fibers [A] in the unidirectional prepreg at an angle of 14° to the longitudinal direction of the reinforcing fibers [A] so that the fiber length of the reinforcing fibers [A] was 25 mm, to obtain a cut prepreg in which discontinuous reinforcing fiber bundles were arranged in one direction. The volume content of the reinforcing fibers [A] in the cut prepreg was adjusted to 60%.

[0133] The cut prepreg was cut into 300mm square pieces, and the orientation of the reinforcing fiber [A] on the surface layer, which is the joining surface, was set to 0°, and the [0° / 90°] 2s After stacking eight sheets so that the surface was mirror symmetric (the symbol s indicates mirror symmetry), a thermoplastic resin [C] sheet was attached to the surface of the joining surface to obtain a fiber-reinforced uncured plastic laminate.

[0134] The uncured fiber-reinforced plastic laminate was placed in a mold with a surface area of ​​300 mm x 300 mm, and a pressure of 0.6 MPa was applied using a press to eliminate voids. The laminate was then heated at 180°C for 2 hours to obtain fiber-reinforced plastic.

[0135] The obtained fiber-reinforced plastic had even less unevenness in thickness than Example 1-1. Furthermore, it was possible to confirm from cross-sectional observation that the region mainly composed of the thermosetting resin [B] and the region mainly composed of the thermoplastic resin [C] flowed to contact each other, forming an interface, and that the thermoplastic resin [C] was impregnated between the discontinuous reinforcing fiber bundles. Furthermore, in all observed regions, the longitudinal ends of the discontinuous reinforcing fiber bundles were in visual contact with the thermosetting resin or thermoplastic resin. At least a portion of the reinforcing fibers constituting the discontinuous reinforcing fiber bundles were in contact with both the thermosetting resin and the thermoplastic resin, and some reinforcing fibers and the thermoplastic resin were in continuous contact with each other in the longitudinal direction from the longitudinal ends of the reinforcing fibers.

[0136] Furthermore, a straight line could be drawn between multiple discontinuous reinforcing fiber bundles, with the total length passing through the thermoplastic resin being 100%. Some of the discontinuous reinforcing fiber bundles located on the surface layer were in contact with both the thermosetting resin and the thermoplastic resin. The resulting fiber-reinforced plastic exhibited sufficient bonding strength.

[0137] <Example 2-2> A fiber-reinforced plastic was obtained in the same manner as in Example 2-1, except that the fiber-reinforced plastic uncured laminate was set in a mold with a surface area of ​​350 mm x 350 mm and stretched by applying a pressure of 3 MPa using a press.

[0138] The obtained fiber-reinforced plastic was thinner than that of Example 2-1, but had little unevenness in thickness. After pressing, the fiber-reinforced plastic was stretched to a 350 mm square without any gaps, exhibiting excellent shape conformability. Furthermore, the impregnation of the thermoplastic resin [C] between the discontinuous reinforcing fiber bundles was clearly visible, and in all observed regions, the longitudinal ends of the discontinuous reinforcing fiber bundles were in contact with both the thermosetting resin and the thermoplastic resin within the visual range. At least a portion of the reinforcing fibers constituting the discontinuous reinforcing fiber bundles were in contact with both the thermosetting resin and the thermoplastic resin, and some reinforcing fibers and the thermoplastic resin were in continuous contact with each other in the longitudinal direction from the longitudinal ends of the reinforcing fibers.

[0139] Furthermore, a straight line could be drawn between multiple discontinuous reinforcing fiber bundles, with the total length passing through the thermoplastic resin being 100%. Some of the discontinuous reinforcing fiber bundles located on the surface layer were in contact with both the thermosetting resin and the thermoplastic resin. The resulting fiber-reinforced plastic exhibited sufficient bonding strength.

[0140] <Comparative Example 1-1> A fiber reinforced plastic was obtained in the same manner as in Example 1-1, except that the thermoplastic resin [C] sheet was not used.

[0141] The obtained fiber reinforced plastic was already in a cured state, so when a test piece for measuring tensile shear bonding strength was prepared, the laminate was not bonded during pressing, and evaluation was not possible.

[0142] <Comparative Example 1-2> Eight SMC prepregs were laminated in the same manner as in Example 1-1 to produce a fiber-reinforced uncured plastic laminate without using a thermoplastic resin [C] sheet.

[0143] The uncured fiber-reinforced plastic laminate was placed in a mold with a surface area of ​​300 mm x 300 mm, and a pressure of 0.6 MPa was applied using a press to eliminate voids, while the laminate was heated at 180°C for 2 hours to obtain a cured product. A thermoplastic resin [C] sheet was then placed on one surface of the cured product and melted at 180°C for 2 hours to bond the thermoplastic resin [C] to the cured product, thereby obtaining a fiber-reinforced plastic.

[0144] The obtained fiber-reinforced plastic had little unevenness in thickness, but there was almost no impregnation of the thermoplastic resin [C] into the discontinuous fiber bundles, and the bonding strength was not sufficient.

[0145] <Comparative Example 2-1> Incised prepregs were laminated in the same manner as in Example 2-2, except that the thermoplastic resin [C] sheet was not used. The fiber-reinforced plastic uncured laminate was set in a mold with a surface area of ​​350 mm × 350 mm and stretched using a press at a pressure of 3 MPa to produce a cured product that did not contain the thermoplastic resin [C]. A thermoplastic resin [C] sheet cut to a size of 350 mm × 350 mm was then placed on one surface of the cured product, set in a mold with a surface area of ​​350 mm × 350 mm, and melted at 180°C for 2 hours using a press at a pressure of 3 MPa to eliminate voids, resulting in a fiber-reinforced plastic.

[0146] After pressing, the cured product was stretched to a 350 mm square with no gaps, demonstrating excellent shape conformability. The resulting fiber-reinforced plastic also had little unevenness in thickness. However, there was little impregnation of the thermoplastic resin [C] between or into the discontinuous fiber bundles, and the bonding strength was insufficient.

[0147] -Evaluation of shape followability <Example 3-1> The cut prepreg produced in Example 2-1 was cut into a 200 mm square sheet with the orientation direction of the reinforcing fiber [A] of the surface layer that becomes the joining surface set at 0° [0° / 90°]. s After laminating the four sheets so as to form the above structure, a thermoplastic resin [C] sheet was attached to the surface layer of one side to obtain a fiber-reinforced plastic uncured laminate.

[0148] The uncured fiber-reinforced plastic laminate was placed in a mold with flat and curved surfaces, with the thermoplastic resin [C] facing up. A pressure of 3 MPa was applied using a press to eliminate voids, and the material was heated at 180°C for 2 hours, yielding a fiber-reinforced plastic with the shape shown in Figure 9.

[0149] Visual inspection of the surface of the bonded surface of the fiber reinforced plastic after pressing revealed no wrinkles or other defects on the curved surface. In addition, there were fewer resin-rich areas at the corners of the curved surface compared to Comparative Example 3-1, which will be described later.

[0150] <Comparative Example 3-1> A fiber reinforced plastic was obtained in the same manner as in Example 3-1, except that no incisions were made.

[0151] When the surface of the joint surface of the obtained fiber-reinforced plastic was visually observed, almost no wrinkles occurred in the curved surface, but there were more resin-rich areas in some areas of the corners of the curved surface than in Example 3-1, and the shape-following ability and uniformity were inferior.

[0152] Table 1 shows an overview of the fiber-reinforced plastics produced in Examples 1-1 to 1-4, 2-1, and 2-2 and Comparative Examples 1-1, 1-2, and 2-1, as well as the evaluation results of the maximum impregnation distance, average roughness height, volume content of reinforcing fibers in the surface layer, and tensile shear bonding strength.

[0153] The maximum impregnation distance, average roughness height, and longitudinal impregnation distance in the examples are values ​​rounded to the nearest whole number, and the maximum impregnation distance and average roughness height shown in the comparative examples are reference values ​​obtained using the surface of the cured product as a reference line because the thermoplastic resin did not reach the reinforcing fibers.

[0154] [Table 1]

[0155] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application (Patent Application No. 2020-126652) filed on July 27, 2020, the contents of which are incorporated herein by reference. [Explanation of symbols]

[0156] 1: Fiber reinforced plastic 2: Discontinuous reinforcing fiber bundle 3: Discontinuous reinforcing fiber 4, 4': Thermoplastic resin 5:Thermosetting resin 6: Interface 7: Cut prepreg 8: Cut 9: Longitudinal direction of reinforcing fiber bundle 10: Direction perpendicular to the longitudinal direction of the reinforcing fiber bundle 11: Reference line 12: Orthobase line 13: Measurement point of impregnation distance 14: Measurement point of roughness mean height 15: Reference line drawn along the side of the reinforcing fiber 16: Measurement point of longitudinal impregnation distance

Claims

1. A fiber-reinforced plastic having a layer containing reinforcing fibers and a matrix in which a thermosetting resin and a thermoplastic resin are integrated as at least one surface layer in the thickness direction, The reinforcing fibers form discontinuous reinforcing fiber bundles that are randomly stacked or that are unidirectionally aligned, A portion of the discontinuous reinforcing fiber bundles is in contact with both the thermosetting resin and the thermoplastic resin, the thermoplastic resin is exposed on at least a portion of the surface of the surface layer, In the surface layer, the average fiber length of the reinforcing fibers is in the range of 5 mm to 100 mm, A fiber-reinforced plastic having a longitudinal impregnation distance of 50 μm or more in the surface layer.

2. The fiber-reinforced plastic according to claim 1 , wherein in the surface layer, an interface is formed between a region containing the thermosetting resin as a main component and a region containing the thermoplastic resin as a main component.

3. In the surface layer, the thermoplastic resin has a continuous region from the surface in a thickness direction, The fiber-reinforced plastic according to claim 1 or 2, wherein the maximum thickness of the portion where the thermoplastic resin contacts the discontinuous reinforcing fiber bundles in the region is 10 μm or more.

4. The fiber-reinforced plastic according to any one of claims 1 to 3, wherein the content of the reinforcing fibers in the surface layer is 15% by volume or more and 70% by volume or less.

5. The fiber-reinforced plastic according to any one of claims 1 to 4, wherein in the surface layer, the reinforcing fiber is at least one selected from the group consisting of carbon fiber and glass fiber.

6. The fiber reinforced plastic according to any one of claims 1 to 5, wherein in the surface layer, an abundance ratio of voids in contact with the longitudinal ends of the discontinuous reinforcing fiber bundles is 5 area% or less.

7. The fiber reinforced plastic according to any one of claims 1 to 6, wherein the thermoplastic resin is present between the discontinuous reinforcing fiber bundles in the surface layer.

8. The fiber reinforced plastic of claim 7 , wherein the thermoplastic resin occupies the spaces between any adjacent discontinuous fiber reinforcement bundles.

9. The discontinuous reinforcing fiber bundles, the thermoplastic resin, and the thermosetting resin are included in both surface layers in the thickness direction, The fiber reinforced plastic according to any one of claims 1 to 8, wherein the thermoplastic resin is exposed on the surfaces of both of the surface layers.

10. The fiber-reinforced plastic according to any one of claims 1 to 9, wherein at least a part of the discontinuous reinforcing fiber bundles constituting the fiber-reinforced plastic is oriented in the out-of-plane direction.

11. A method for producing a fiber-reinforced plastic according to any one of claims 1 to 10, Step 1: impregnating a reinforcing fiber bundle with a thermosetting resin; Step 2: impregnating the reinforcing fiber bundle with a thermoplastic resin; Step 3: Cutting the reinforcing fiber bundles into discontinuous reinforcing fiber bundles; A step 4 of stacking a required number of substrates constituting a fiber reinforced plastic so that the thermoplastic resin is exposed on at least one surface in the thickness direction; and step 5 of molding the fiber reinforced plastic by heating and pressing, The step 5 is performed after the steps 1 to 4 are performed, or the step 5 is performed simultaneously with the step 2 after the steps 1, 3, and 4 are performed, or the step 5 is performed simultaneously with the step 2 after the steps 2, 3, and 4 are performed. A method for producing a fiber-reinforced plastic.

12. 12. The method for producing a fiber-reinforced plastic according to claim 11, further comprising step 6 of flowing the discontinuous reinforcing fiber bundles so that the longitudinal ends of the discontinuous reinforcing fiber bundles come into contact with the thermosetting resin or the thermoplastic resin in the surface layer where the thermoplastic resin is exposed.

13. In step 6, In the surface layer where the thermoplastic resin is exposed, at least a part of the discontinuous reinforcing fiber bundles is in contact with both the thermosetting resin and the thermoplastic resin, And at least one of the reinforcing fibers constituting the reinforcing fiber bundle and the thermoplastic resin are caused to flow so as to be continuously in contact with each other in the longitudinal direction from the longitudinal end of the reinforcing fiber, The method for producing a fiber-reinforced plastic according to claim 11 or 12.

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