Reinforced fiber substrate

Abstract

The present invention provides a reinforced fiber substrate having a resin material layer containing thermoplastic resin fibers, wherein the occurrence of microcracks caused by the resin material layer is reduced. [Solution] The present invention aims to provide a reinforced fiber substrate having a resin material layer containing thermoplastic resin fibers, wherein the occurrence of microcracks caused by the resin material layer is reduced. The present invention relates to a reinforced fiber substrate 30 having one or more reinforced fiber layers 330, 340, 350 containing reinforced fibers, one or more resin material layers 310 to 316 containing thermoplastic resin fibers, and auxiliary threads, wherein the auxiliary threads maintain the integrity of the reinforced fiber layers and / or the reinforced fiber substrate by connecting the reinforced fibers and / or the reinforced fiber layers, and the average fiber diameter of the thermoplastic resin fibers is 0.5 μm to 35 μm.

Description

[Technical Field]

[0001] This invention relates to a reinforced fiber substrate. More particularly, it relates to a reinforced fiber substrate, a preform material containing a reinforced fiber substrate, and a fiber-reinforced resin composite material having a reinforced fiber substrate. [Background technology]

[0002] Fiber-reinforced resin composite materials (also called fiber-reinforced composites or composites) are lightweight, high-strength, and highly rigid, making them widely used in sports and leisure applications such as fishing rods and golf shafts, as well as in industrial applications such as automobiles and aircraft. Methods for molding fiber-reinforced resin composite materials include molding prepregs (intermediate materials) which are formed into sheets by impregnating a reinforcing fiber substrate with resin beforehand, and a method (resin transfer molding method, RTM method) in which liquid resin (i.e., uncured curable resin or molten thermoplastic resin) is impregnated into a reinforcing fiber substrate placed in a mold, and then cured or solidified to obtain fiber-reinforced resin composite materials.

[0003] Reinforced fiber substrates often have multiple reinforced fiber layers (particularly reinforced fiber sheets). Examples of reinforced fiber layers include fabrics woven with reinforced fibers as warp and weft threads in plain weave or satin weave. In such fabrics, for example, the reinforced fibers as warp threads and the reinforced fibers as weft threads extend perpendicularly to each other.

[0004] In contrast, a unidirectional (UD) reinforcing fiber layer, in which the reinforcing fibers are aligned in one direction, can be used. An example of such a unidirectional reinforcing fiber layer is a unidirectional woven fabric. A unidirectional woven fabric is a fabric composed of reinforcing fibers aligned in one direction as warp threads and auxiliary threads as weft threads, and is a so-called bamboo blind woven fabric.

[0005] Furthermore, non-crimp fabric can also be used as the reinforcing fiber base material. In non-crimp fabric, multiple layers of reinforcing fiber, each consisting of reinforcing fibers aligned in one direction, are laminated together, and these laminated reinforcing fiber layers are sewn together with auxiliary stitching threads. In other words, in non-crimp fabric, a laminate of reinforcing fiber sheets, each consisting of reinforcing fibers aligned in one direction, is integrated by being sewn together with auxiliary threads (particularly called stitching threads) that penetrate the laminate in the thickness direction.

[0006] When fiber-reinforced resin composite materials are manufactured from these reinforced fiber substrates containing auxiliary threads, microcracks may occur. In particular, microcracks are known to occur around the stitching threads used as auxiliary threads. These microcracks can gradually propagate and degrade the mechanical properties of the fiber-reinforced composite material. Various studies are being conducted to suppress the occurrence of such microcracks.

[0007] Patent Document 1 describes an intermediate product in which at least two layers of unidirectional reinforcing fibers are bonded together by a sewing thread or knitting thread, and describes a sewing thread or knitting thread having a count of 30 dTex or less.

[0008] Patent Document 2 discloses a reinforced fiber stitch base material in which a reinforced fiber sheet made of reinforcing fibers is stitched together with stitching thread, and regarding the stitching thread, the coefficient of linear expansion in the fiber axial direction after heating at 180°C for 2 hours and then cooling is -1 × 10 -6 ~70×10 -6 It states that it is / K.

[0009] Patent Document 3 also discloses a reinforced fiber stitch base material, which is made of a reinforced fiber sheet made of reinforcing fibers that are stitched together with stitching thread, and describes a stitching thread to which an organic compound having a polar group is attached.

[0010] Non-Patent Document 1 discloses suppressing the formation of microcracks by reducing the resin-rich portion in the fiber-reinforced composite material as much as possible and improving the toughness of the interface between the stitch yarn and the matrix resin.

[0011] Further, the reinforcing fiber base material can have a resin material layer containing thermoplastic resin fibers. As such a resin material layer, for example, a non-woven fabric containing thermoplastic resin fibers can be disposed above and / or between the reinforcing fiber layers (see, for example, Patent Document 2). Such a resin material layer is also called a veil or a reinforcing veil and can improve the impact resistance of the reinforcing fiber base material.

[0012] Patent Document 4 describes using a polyamide having a melting point of 165°C or higher and 180°C or lower as a binder in the form of a non-woven fabric. According to this document, it is said that the impact resistance and microcrack resistance of the fiber-reinforced composite material obtained in combination with the reinforcing fibers can be improved.

Prior Art Documents

Patent Documents

[0013]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Non-Patent Documents

[0014]

Non-Patent Document 1

Summary of the Invention

[0015] As described above regarding the prior art, microcracks can be reduced by selecting auxiliary threads. However, in reinforced fiber substrates having the resin material layer described above, when attempting to reduce microcracks by selecting auxiliary threads, there were cases where the microcracks were not sufficiently reduced.

[0016] While investigating measures to suppress the occurrence of microcracks in a reinforced fiber substrate having the resin material layer described above, the inventors of this case found that in order to sufficiently reduce microcracks, it is important to reduce microcracks caused by the resin material layer, particularly the thermoplastic resin fibers constituting the resin material layer, in addition to microcracks caused by auxiliary threads (especially stitching threads), which have been the subject of conventional studies.

[0017] Therefore, an object of the present invention is to provide a reinforced fiber substrate having a resin material layer containing thermoplastic resin fibers, wherein the occurrence of microcracks caused by the resin material layer is reduced. [Means for solving the problem]

[0018] The object of the present invention is solved by the present invention having the following aspects.

[0019] <Aspect 1> One or more reinforcing fiber layers containing reinforcing fibers, One or more resin material layers containing thermoplastic resin fibers, and auxiliary thread A reinforced fiber substrate having, The auxiliary threads connect the reinforcing fibers to each other and / or the reinforcing fiber layers to each other, thereby maintaining the integrity of the reinforcing fiber layer and / or the reinforcing fiber base material, and The average fiber diameter of the thermoplastic resin fibers is 0.5 μm to 35 μm. Reinforced fiber base material. <Aspect 2> The reinforced fiber substrate according to embodiment 1, wherein the resin material layer is made of a nonwoven fabric containing thermoplastic resin fibers. <Aspect 3> The reinforcing fiber substrate according to embodiment 1 or 2, wherein the thermoplastic resin fiber has a melting point in the range of 130°C to 230°C. <Aspect 4> The reinforced fiber substrate according to any one of embodiments 1 to 3, wherein the thermoplastic resin fiber is a fiber of polyamide resin, polyester resin, polyethersulfone (PES) resin, or polyetherimide (PEI) resin. <Aspect 5> The reinforced fiber base material according to any one of embodiments 1 to 4, wherein the reinforced fiber layer is a unidirectional fabric having the reinforced fibers aligned in one direction as warp threads and the auxiliary threads as weft threads. <Aspect 6> The reinforcing fiber base material includes at least two reinforcing fiber layers that are laminated in an overlapping manner, each of the at least two reinforcing fiber layers is composed of reinforcing fibers aligned in one direction, and the at least two reinforcing fiber layers are sewn together by stitching thread as auxiliary thread. A reinforced fiber substrate according to any one of embodiments 1 to 5. <Aspect 7> The reinforced fiber substrate according to embodiment 6, wherein the direction of extension of the reinforcing fibers constituting one of the at least two reinforcing fiber layers is different from the direction of extension of the reinforcing fibers constituting the other reinforcing fiber layer. <Aspect 8> The reinforced fiber substrate according to any one of embodiments 1 to 7, wherein each of the one or more resin material layers is disposed on the surface of any of the reinforced fiber layers. <Pattern 9> The reinforcing fiber substrate according to any one of embodiments 1 to 8, wherein at least one of the resin material layers is disposed between the two reinforcing fiber layers. <Aspect 10> The auxiliary thread used as stitching thread has a fineness of 1 to 75 dtex and / or, Having 1 to 50 filaments, A reinforced fiber substrate according to any one of embodiments 1 to 9. <Aspect 11> The reinforced fiber substrate according to any one of embodiments 1 to 10, wherein the auxiliary yarn is made of resin fibers having a melting point of 80 to 185°C. <Aspect 12> The reinforced fiber substrate according to any one of embodiments 1 to 11, wherein the auxiliary yarn comprises fibers of polyamide resin, polyester resin, polyethersulfone (PES) resin, or polyetherimide (PEI) resin. <Aspect 13> The reinforcing fiber substrate according to any one of embodiments 1 to 12, wherein the auxiliary yarn contains a compound having at least one selected from the group consisting of a hydroxyl group, an amino group, a phenol group, a lactam group, and an epoxy group, as well as an amide bond and an ester bond. <Aspect 14> The auxiliary yarn is one that melts when heated at 180°C for 2 hours, or the coefficient of linear expansion in the fiber axis direction of the auxiliary yarn after heating at 180°C for 2 hours and then cooling is -1 × 10⁻¹⁰ -6 ~80×10 -6 A reinforced fiber substrate according to any one of embodiments 1 to 13, wherein the material is / K. <Aspect 15> A preform material comprising a reinforcing fiber base material according to any one of embodiments 1 to 14, and 1 to 20 parts by mass of binder resin per 100 parts by mass of the reinforcing fiber base material. <Aspect 16> A method for producing a preform, comprising heating a composite containing a reinforcing fiber substrate and a binder resin according to any one of embodiments 1 to 14 under pressure. <Aspect 17> A fiber-reinforced resin composite material comprising a reinforced fiber substrate according to any one of embodiments 1 to 14, and a matrix resin impregnated in the reinforced fiber substrate. <Aspect 18> A method for producing a fiber-reinforced composite material, comprising impregnating a reinforcing fiber substrate described in any one of embodiments 1 to 14 with a matrix resin. [Effects of the Invention]

[0020] According to the present invention, it is possible to provide a reinforced fiber substrate having a resin material layer containing thermoplastic resin fibers, wherein the occurrence of microcracks caused by the resin material layer is reduced. [Brief explanation of the drawing]

[0021] [Figure 1] Figure 1 shows a schematic cross-sectional view of a reinforced fiber substrate according to one embodiment of the present invention. [Figure 2] Figure 2 shows a schematic perspective view of the reinforcing fiber layer in Figure 1. [Figure 3] Figure 3 shows a schematic cross-sectional view of a reinforced fiber substrate according to another embodiment of the present invention. [Figure 4] Figure 4 shows a perspective view of the multiple reinforcing fiber layers in Figure 3. [Modes for carrying out the invention]

[0022] ≪Reinforced fiber base material≫ The reinforced fiber substrate relating to this disclosure is One or more reinforcing fiber layers containing reinforcing fibers, One or more resin material layers containing thermoplastic resin fibers, and auxiliary thread It has, The auxiliary threads connect the reinforcing fibers to each other and / or the reinforcing fiber layers to each other, thereby maintaining the integrity of the reinforcing fiber layer and / or the reinforcing fiber base material, The average fiber diameter of thermoplastic resin fibers is between 0.5 μm and 35 μm.

[0023] As described above, the inventors of this invention focused on microcracks caused by the resin material layer in a reinforced fiber substrate having a resin material layer containing thermoplastic resin fibers, in order to sufficiently reduce microcracks.

[0024] Microcracks, in this context, are tiny cracks ranging from a few to tens of micrometers in size that can occur, particularly in fiber-reinforced composite materials used in aerospace applications. These microcracks are more likely to occur in environments where thermal shock cycles involving rapid temperature changes between high temperatures of around 70-100°C and low temperatures of around -50-60°C are repeated hundreds of times or more. As the temperature changes from high to low, the matrix resin in fiber-reinforced composite materials tends to shrink, but the deformation of the matrix resin is suppressed by the reinforcing fibers, which have a relatively low coefficient of thermal expansion compared to the matrix resin. As a result, residual thermal stress accumulates within the matrix resin. Microcracks are likely to occur due to the accumulation of fatigue stress caused by these thermal shock cycles. Similarly, auxiliary threads and nonwoven fabric fibers in the reinforcing fiber substrate often have different coefficients of thermal expansion than the matrix resin. Residual thermal stress concentrates at the interface of fiber-reinforced composite materials containing these fibers, making them prone to interfacial delamination and microcracks originating from the interface.

[0025] According to the reinforced fiber substrate of the present invention, the occurrence of microcracks can be suppressed in a reinforced fiber substrate having a resin material layer. Although there is no intention to limit the theory, in the reinforced fiber substrate of the present invention, the average fiber diameter of the thermoplastic resin fibers contained in the resin material layer is relatively small, so the absolute value of the volume change of the thermoplastic resin fibers due to the thermal shock cycle and the residual thermal stress generated per unit interface between the matrix resin and the thermoplastic resin fibers are small, and as a result, the occurrence of microcracks caused by the resin material layer is reduced.

[0026] Furthermore, the present invention offers particularly advantageous effects in reinforced fiber substrates in which microcracks caused by improved auxiliary threads (e.g., stitching threads) are reduced. Although there is no intention to limit the theory, it is thought that when auxiliary threads with relatively poor microcrack resistance are used, the frequency of microcracks caused by the auxiliary threads is relatively high. In contrast, in reinforced fiber substrates using auxiliary threads with improved microcrack resistance, while microcracks caused by the auxiliary threads are reduced, it is thought that microcracks caused by the resin material layer are more likely to occur. As described above, the present invention can suppress the occurrence of such microcracks.

[0027] Furthermore, the reinforced fiber substrate according to the present invention may provide a composite (fiber-reinforced resin composite material) with improved impact resistance. Although there is no intention to limit the theory, in the reinforced fiber substrate according to the present invention, the fiber diameter of the thermoplastic resin fibers contained in the resin material layer is relatively small, which improves the interface ratio per unit volume between the thermoplastic resin fibers and the matrix resin. This improved interface ratio efficiently absorbs the energy generated between the layers of the fiber-reinforced composite material due to external impact, thereby suppressing the propagation of interlayer cracks, and as a result, the post-impact strength of the composite is thought to be improved.

[0028] <Reinforced fiber base material> The reinforced fiber substrate according to this disclosure comprises one or more reinforced fiber layers containing reinforcing fibers, one or more resin material layers containing thermoplastic resin fibers, and auxiliary yarns.

[0029] To facilitate understanding of the present invention, an exemplary structure of the reinforcing fiber substrate according to this disclosure will be schematically described with reference to the drawings. The drawings are schematic diagrams for facilitating understanding of the present invention, are not to scale, and do not limit the present invention.

[0030] Figure 1 shows a schematic cross-sectional view of the minimum configuration of a reinforced fiber substrate 10 according to one embodiment of the present invention. The reinforced fiber substrate 10 includes a resin material layer 110 and a reinforced fiber layer 130 that are laminated in an overlapping manner. The resin material layer 110 is arranged on the surface of the reinforced fiber layer 130. The resin material layer 110 includes thermoplastic resin fibers. The resin material layer 110 may be a nonwoven fabric made of thermoplastic resin fibers. The reinforced fiber layer 130 consists of reinforced fibers aligned in one direction. Auxiliary threads (not shown) can play a role in maintaining the integrity of the reinforced fiber layer and / or the reinforced fiber substrate by connecting the reinforced fibers to each other and / or the reinforced fiber layers to each other.

[0031] Figure 2 shows a schematic perspective view of the reinforcing fiber layer 130 in Figure 1. The resin material layer 110 is not shown in Figure 2. In the embodiment of Figure 2, the reinforcing fiber layer 130 is a unidirectional woven fabric (UD-woven fabric). A unidirectional woven fabric is a so-called "bamboo blind woven fabric" and is composed of reinforcing fibers (especially bundles of reinforcing fibers) 22 and auxiliary threads 24 that are aligned in one direction. The reinforcing fibers 22 as warp threads and the auxiliary threads 24 as weft threads intersect with each other to form the fabric.

[0032] Although Figures 1 and 2 illustrate the minimum configuration of a reinforced fiber substrate having one reinforcing fiber layer and one resin material layer, the reinforced fiber substrate may also have multiple reinforcing fiber layers and / or resin material layers. For example, the resin material layer may be laminated between multiple reinforcing fiber layers.

[0033] Figure 3 shows a schematic cross-sectional view of a reinforced fiber substrate 30 according to another embodiment of the present invention. The reinforced fiber substrate 30 includes a plurality of laminated resin material layers 310 to 316 and a plurality of reinforced fiber layers 330, 340, and 350. Resin material layers 312 and 314 are arranged between the layers of reinforced fiber layers 330, 340, and 350, respectively. Resin material layers 310 and 316 are arranged as the outermost layers. Resin material layers 310 to 316 may be nonwoven fabrics composed of thermoplastic resin fibers. Reinforced fiber layers 330, 340, and 350 consist of reinforced fibers aligned in one direction. Auxiliary threads (not shown) can connect the reinforcing fibers of the reinforcing fiber layers 330, 340, and 350 to each other, and / or connect the reinforcing fiber layers 330, 340, and 350 to each other, thereby maintaining the shape (particularly the sheet shape) of the reinforcing fiber layers 330, 340, and 350 and the integrity of the reinforcing fiber base material 30.

[0034] Figure 4 is a perspective view corresponding to the reinforcing fiber substrate in Figure 3. In Figure 4, the resin material layers 310-316 are not shown. The multiple reinforcing fiber layers 330, 340, and 350 in Figure 4 constitute the non-crimp fabric 40. That is, each of the reinforcing fiber layers 330, 340, and 350 is formed from reinforcing fibers 42 aligned in one direction, and these laminated reinforcing fiber layers are integrated by being sewn together with stitching threads 44 as auxiliary threads. The stitching threads 44 as auxiliary threads can extend continuously in the thickness direction of the laminate across the multiple reinforcing fiber layers. For simplicity, only a portion of the auxiliary threads are shown in Figure 4. In non-crimp fabrics, bending of the reinforcing fibers is less likely to occur, so the mechanical properties of fiber-reinforced composite materials manufactured from reinforcing fiber substrates can be further improved.

[0035] In the embodiment shown in Figure 4, the extension direction of the reinforcing fibers constituting each of the multiple reinforcing fiber layers is different. Specifically, the reinforcing fibers constituting the reinforcing fiber layer 330 extend along the direction L shown in Figure 4, the reinforcing fibers constituting the reinforcing fiber layer 340 extend at an angle of approximately 90° with respect to direction L, and the reinforcing fibers constituting the reinforcing fiber layer 350 extend at an angle of approximately 45° with respect to direction L.

[0036] The resin material layers 310-316, placed on top of the reinforcing fiber layers, can also be sutured together with multiple reinforcing fiber layers using auxiliary threads 44.

[0037] The reinforced fiber substrate relating to this disclosure preferably has a density of 100 to 2000 g / m². 2 Comfortable 150~1500g / m 2 It has a basis weight of [value]. Furthermore, the thickness of the reinforcing fiber base material according to this disclosure can be appropriately selected depending on the application of the molded product, but may be 0.1 to 2 mm or 0.5 to 1.5 mm.

[0038] <Resin material layer> The reinforced fiber substrate relating to this disclosure has a resin material layer containing thermoplastic resin fibers.

[0039] In one preferred embodiment of the present disclosure, the resin material layer is a sheet containing thermoplastic resin fibers, particularly a nonwoven fabric containing thermoplastic resin fibers.

[0040] The resin material layer can be laminated together with the reinforcing fiber layer to form a laminate, as illustrated in Figures 1 and 3. In such a laminate, the resin material layer may be positioned between the reinforcing fiber layers. Preferably, the resin material layer is adjacent to the reinforcing fiber layer, and in particular, positioned on the surface of the reinforcing fiber layer. The presence of the resin material layer in the reinforcing fiber substrate can improve the impact resistance of the fiber-reinforced resin composite material produced from the reinforcing fiber substrate. The reinforcing fiber layer and the resin material layer may be bonded together with a binder. For information on the binder, refer to the description of the preform material described later.

[0041] If the reinforcing fiber layer is a unidirectional fabric, the resin material layer may be placed, for example, on the main surface of the unidirectional fabric.

[0042] When the reinforcing fiber base material has a non-crimped fabric, the resin material layer may be placed in the outermost layer (i.e., for example, on one or both sides of the main surface of a laminate consisting of multiple reinforcing fiber layers), and / or between the multiple reinforcing fiber layers constituting the non-crimped fabric.

[0043] The resin material layer (particularly nonwoven fabric) preferably has a thickness of 1 μm to 50 μm, more preferably 2 μm to 40 μm, and even more preferably 3 μm to 35 μm.

[0044] (Thermoplastic resin fiber) According to the present invention, the resin material layer includes thermoplastic resin fibers having an average fiber diameter of 0.5 μm to 35 μm (hereinafter also referred to as "small-diameter thermoplastic resin fibers").

[0045] The mass percentage of thermoplastic resin fibers having an average fiber diameter of 0.5 μm to 35 μm is preferably 50% by mass or more, more preferably 80% by mass or more, and particularly preferably 90% by mass or more, relative to the resin material layer. In particular, the resin material layer consists of thermoplastic resin fibers having an average fiber diameter of 0.5 μm to 35 μm.

[0046] The average fiber diameter of these small thermoplastic resin fibers is preferably 0.5 μm to 34 μm, 0.5 μm to 32 μm, 0.5 μm to 30 μm, 1 μm to 25 μm, or 1 μm to 20 μm, more preferably 2 μm to 15 μm, particularly preferably 3 μm to 12 μm, and most preferably 4 μm to 8 μm.

[0047] The average fiber diameter of small thermoplastic resin fibers can be determined by averaging the fiber diameter values ​​measured for at least 30 fibers using an optical microscope.

[0048] For the average fiber diameter of the small-diameter thermoplastic resin fibers, it is preferable that the coefficient of variation of the fiber diameter is reduced, and more preferably that the coefficient of variation of the fiber diameter is 0.20 or less. Furthermore, it is particularly preferable that the coefficient of variation of the fiber diameter is 0.18 or less, 0.16 or less, 0.14 or less, 0.12 or less, or 0.10 or less. Since a reduced coefficient of variation of the fiber diameter is preferable, the lower limit is not particularly limited, but it may be, for example, 0.01 or more, 0.02 or more, or 0.05 or more. When the coefficient of variation of the fiber diameter is reduced, the proportion of relatively large-diameter fibers is reduced, so it is thought that the occurrence of cracks can be suppressed or avoided particularly well. By manufacturing nonwoven fabric by the melt-blown method, the coefficient of variation of the fiber diameter of the fibers contained in the nonwoven fabric can be reduced particularly well.

[0049] The coefficient of variation of fiber diameter can be measured by measuring the fiber diameter using an optical microscope.

[0050] The small-diameter thermoplastic resin fibers preferably have a melting point in the range of 130°C to 230°C, and particularly preferably in the range of 160°C to 230°C. Even when the small-diameter thermoplastic resin fibers according to the present invention have a relatively high melting point (particularly 185°C to 230°C, 190°C to 230°C, or 195°C to 225°C), they exhibit good microcrack resistance. When small-diameter thermoplastic resin fibers with a relatively high melting point are used, the resin material layer can maintain its shape during the manufacturing process of the fiber-reinforced composite material, effectively suppressing crack propagation and potentially further improving impact resistance. Furthermore, when small-diameter thermoplastic resin fibers with a relatively high melting point are used, the heat resistance of the resulting fiber-reinforced composite material is improved, and the mechanical properties of the fiber-reinforced composite material in high-temperature environments may be further enhanced.

[0051] The melting point of thermoplastic resin fibers can be measured using a differential scanning calorimetry device according to the following conditions, based on the standard JIS K7121: Measurement temperature range: Room temperature to 250℃ Heating rate: 5°C / min

[0052] The fine-diameter thermoplastic resin fibers are preferably fibers of a polyolefin resin, a polyamide resin, a polyester resin, a cellulose fiber, a polyethersulfone (PES) resin, or a polyetherimide (PEI) resin, and particularly preferably fibers of a polyamide resin. Examples of the polyamide (PA) resin include PA6, PA12, PA11, PA6-6, PA6-10, PA6-12, PA10-10, and PA6 / PA12 copolymers. From the viewpoint of heat resistance, fibers containing an aromatic compound are preferred.

[0053] Preferably, the resin material layer is composed of continuous fibers. Also preferably, the basis weight of the resin material layer is 1 g / m 2 ~15 g / m 2 , more preferably 2 g / m 2 ~10 g / m 2 , and particularly preferably 4 g / m 2 ~6 g / m 2 is.

[0054] (Non-woven fabric composed of fine-diameter thermoplastic resin fibers) In one embodiment according to the present disclosure, the resin material layer is a non-woven fabric containing thermoplastic resin fibers having an average fiber diameter of 0.5 μm to 35 μm, and more preferably a non-woven fabric made of thermoplastic resin fibers having an average fiber diameter of 0.5 μm to 35 μm. Such a non-woven fabric can be produced particularly by the melt blowing method. By using the melt blowing method, a non-woven fabric containing thermoplastic resin fibers with a finer fiber diameter can be produced as compared with the case of using the spunbond method.

[0055] <Reinforcing fiber layer> The reinforcing fiber layer contains reinforcing fibers.

[0056] In one embodiment of the present disclosure, the reinforcing fiber layer is unidirectional (UD). That is, the reinforcing fiber layer is formed from reinforcing fibers aligned in one direction. As the reinforcing fiber layer, for example, a reinforcing fiber sheet can be used, and in particular, a reinforcing fiber sheet obtained by processing a continuous bundle of reinforcing fibers into a sheet can be used. The reinforcing fiber layer is particularly a unidirectional woven fabric as described above with reference to the drawings, or multiple reinforcing fiber layers constitute a non-crimped fabric.

[0057] In other words, in one embodiment, the reinforcing fiber layer is a unidirectional fabric having reinforcing fibers aligned in one direction as warp threads and auxiliary threads as weft threads.

[0058] Another embodiment includes a non-crimped fabric, in which the reinforcing fiber base material includes at least two reinforcing fiber layers that are laminated in an overlapping manner, each of the at least two reinforcing fiber layers being composed of reinforcing fibers aligned in one direction, and the at least two reinforcing fiber layers are sewn together with stitching thread as an auxiliary thread.

[0059] Preferably, in the reinforced fiber substrate according to this disclosure, the direction of extension of the reinforcing fibers in one of the at least two reinforcing fiber layers differs from the direction of extension of the reinforcing fibers in the other reinforcing fiber layer. In particular, a plurality of reinforcing fiber layers, each consisting of reinforcing fibers aligned in one direction, are sequentially laminated with their fiber axis directions alternating. This embodiment is preferable because it improves the isotropy of the reinforced fiber substrate.

[0060] (Reinforced fiber) Examples of reinforcing fibers include carbon fibers, glass fibers, aramid fibers, boron fibers, and metal fibers. The reinforcing fiber is preferably carbon fiber.

[0061] The average length of the reinforcing fibers is not particularly limited, but may be, for example, 5 cm to 100 m.

[0062] <Auxiliary thread> The auxiliary yarn of this disclosure plays a role in maintaining the integrity of the reinforcing fiber layer and / or the reinforcing fiber base material by connecting the reinforcing fibers with each other and / or the reinforcing fiber layers with each other.

[0063] In one embodiment, auxiliary threads constitute the weft threads to reinforcing fibers that act as warp threads. For example, a unidirectional fabric is formed when auxiliary threads, acting as weft threads, intersect reinforcing fibers that are aligned in one direction at an angle of approximately 90°.

[0064] In one embodiment, the auxiliary thread is a stitching thread. The method of stitching the reinforcing fiber substrate with the stitching thread is not particularly limited, but the stitching thread is used, for example, to sew together multiple reinforcing fiber layers in a laminate in which multiple reinforcing fiber layers made of reinforcing fibers aligned in one direction are stacked.

[0065] When auxiliary threads are used as stitching threads, they preferably have a fineness of 1 dtex to 75 dtex, more preferably 15 dtex to 40 dtex. Furthermore, the auxiliary threads preferably have a single-fiber diameter of 10 to 40 μm. The auxiliary threads preferably have 1 to 50 filaments (single threads), more preferably 4 to 24 filaments. When auxiliary threads satisfying at least one of these conditions are used, the occurrence of microcracks at the interface between the auxiliary threads and the matrix resin in a composite containing a reinforcing fiber substrate may be suppressed.

[0066] In one preferred embodiment of the present invention, the auxiliary thread is composed of resin fibers having a melting point of 80 to 185°C, particularly 85 to 175°C. By using such an auxiliary thread, it may be possible to suppress the occurrence of microcracks at the interface between the auxiliary thread and the matrix resin.

[0067] In one preferred embodiment of the present invention, the auxiliary yarn comprises polyolefin fibers, polyamide resins, polyester resins, cellulose fibers, polyethersulfone (PES) resins, or polyetherimide (PEI) resins, or mixtures thereof. Alternatively, the auxiliary yarn may consist of at least one of these. From the viewpoint of heat resistance, it is preferable to use fibers made of aromatic compounds, and more preferable to use fibers made of all aromatic compounds.

[0068] In one preferred embodiment of the present invention, the auxiliary yarn comprises a compound having a polar group and / or polar bond, particularly a compound having at least one selected from the group consisting of a hydroxyl group, an amino group, a phenol group, a lactam group, an epoxy group, an amide bond, and an ester bond. For example, a fiber formed from a compound having a polar group and / or polar bond in its chemical structure can be used as the material for the auxiliary yarn. Alternatively, an organic compound having a polar group and / or polar bond may be attached to the auxiliary yarn.

[0069] When the auxiliary thread has polar groups and / or polar bonds, it exhibits excellent affinity with the matrix resin, thereby suppressing delamination at the interface between the auxiliary thread and the matrix resin, and further suppressing the occurrence of microcracks at the interface between the auxiliary thread and the matrix resin.

[0070] In particular, when using a thermosetting resin as the matrix resin, if reactive groups such as hydroxyl groups, amino groups, and epoxy groups are used as polar groups, the reactive groups contained in the fibers react with the thermosetting resin at the interface between the matrix resin and the fibers during the manufacturing process of the fiber-reinforced composite material, forming covalent bonds. This can result in higher interfacial adhesion between the auxiliary yarn and the matrix resin.

[0071] In one preferred embodiment of the present invention, the auxiliary yarn has a coefficient of linear expansion in the fiber axial direction of -1 × 10⁻¹⁰ after being heated at 180°C for 2 hours and then cooled. -6 ~80×10 -6The auxiliary yarn is either / K or melts upon heating at 180°C for 2 hours. In this case, the occurrence of microcracks at the interface between the auxiliary yarn and the matrix resin can be suppressed in a composite containing a reinforcing fiber base material.

[0072] The coefficient of linear expansion of the auxiliary yarn is the coefficient of linear expansion measured in the temperature range of -50°C to 70°C. More preferably, the coefficient of linear expansion is -1 × 10⁻⁶. -6 ~70×10 -6 / K, even more comfortably 5×10 -6 ~50×10 -6 / K, particularly preferably 10×10 -6 ~30×10 -6 It is / K. The coefficient of linear expansion can be measured as follows: After heating the fiber sample at 180°C for 2 hours without applying tension and then cooling, the coefficient of linear expansion in the linear axis direction is measured using a thermomechanical analyzer under the following measurement conditions. Cooling after heating at 180°C for 2 hours can be performed by allowing the heated sample to stand at 25°C for slow cooling (especially natural cooling). [Measurement conditions] Temperature at which heating begins: -60℃ Measurement temperature range: -50 to 70°C Heating end temperature: 100℃ Heating rate: 5°C / min Load: 0.0001N

[0073] Furthermore, the coefficient of linear expansion (CTEm(×10)) of the matrix resin used when creating fiber-reinforced composite materials. -6 It is preferable that the linear expansion coefficient of the stitching thread be less than or equal to CTEm(×10) -6 / K)~(CTEm-30)(×10 -6 It is preferable that the coefficient of thermal expansion of the stitching thread be within the range of (CTEf(×10)) of the coefficient of thermal expansion of the reinforcing fibers used in the reinforcing fiber sheet. -6 It is also preferable that the value be greater than or equal to / K), CTEf(×10 -6 / K)~(CTEf+30)(×10 -6It is preferable to set the range to / K).

[0074] In the reinforced fiber substrate relating to this disclosure, the amount of auxiliary yarn is 1 to 10 g / m 2 It is fine if it is 2-5 g / m 2 It is preferable that it be so.

[0075] <Preform material> When molding a fiber-reinforced composite material using the reinforced fiber substrate of the present invention, the reinforced fiber substrate can be used as is, but from the viewpoint of handling and workability, it is preferable to use a preform material that has been pre-molded by stacking the reinforced fiber substrates.

[0076] Preform material can be manufactured by a method that includes a step of heating a composite (particularly a composite composed of these) containing a reinforcing fiber base material and a binder resin under pressure. For example, preform material is manufactured by stacking the reinforcing fiber base material of the present invention, or the reinforcing fiber base material of the present invention and other reinforcing fiber base materials, on one side of a preform mold to a desired thickness, scattering powder of a binder resin (binder resin) or laminating resin sheets as needed, and pre-forming by heating under pressure using a press with a heating plate or the like. The resin melts upon heating, and the reinforcing fiber base materials of the present invention, or the reinforcing fiber base material of the present invention and other reinforcing fiber sheets, are molded according to the mold, resulting in a preform material that maintains the shape of the mold. Furthermore, by pressurizing the preform material, the laminate of reinforcing fibers becomes more tightly packed, thereby improving the morphological stability of the preform material. In addition, by reducing the bulk of the preform material through pressurization, a fiber-reinforced composite material with a high reinforcing fiber volume ratio and excellent mechanical properties can be obtained. The preferred temperature range for manufacturing preform material depends on the type of resin material used as the binder resin, but by heating under pressure to preferably 50°C to 200°C, more preferably 60°C to 180°C, and even more preferably 70°C to 160°C, it is easier to obtain preform material with a reinforcing fiber volume ratio in the range of 45°C to 62%, and a fiber-reinforced composite material with stable quality can be obtained.

[0077] There are no particular restrictions on the resin material used as the binder resin. Thermosetting resins such as epoxy resins and vinyl ester resins, thermoplastic resins such as polyamides and polyethersulfones, and mixtures thereof can be used as appropriate. These resins may be used by scattering them as powder, or they may be formed into sheets or nonwoven fabrics and laminated onto the reinforced fiber substrate of the present invention. Alternatively, they may be pre-attached to each filament constituting the reinforced fiber substrate of the present invention.

[0078] The amount of binder resin constituting the preform material is preferably 1 to 20 parts by mass, and more preferably 5 to 10 parts by mass, per 100 parts by mass of the reinforced fiber base material of the present invention. The thickness of the preform material varies depending on the intended use, but is preferably 1 to 40 mm.

[0079] The preform material can be transformed into a fiber-reinforced composite material by known molding methods such as the RTM method or the RFI method. The preform material produced by the above method retains its three-dimensional shape even after preformation. Therefore, it is possible to move the preform material from the preform mold to the fiber-reinforced composite material mold without distorting its shape. Consequently, it is not necessary to directly laminate the preform material into the mold for producing the fiber-reinforced composite material, which reduces the mold occupancy time and improves the productivity of the fiber-reinforced composite material.

[0080] Fiber-reinforced composite materials A fiber-reinforced resin composite material (also called fiber-reinforced plastic, FRP; or composite) can be manufactured from the reinforcing fiber substrate and the matrix resin impregnated in the reinforcing fiber substrate.

[0081] The fiber-reinforced resin composite material comprises, or substantially consists of, a reinforcing fiber substrate and a matrix resin according to the present disclosure.

[0082] A method for producing a fiber-reinforced composite material according to this disclosure may include a step of impregnating a reinforcing fiber substrate according to this disclosure with a matrix resin. For example, a fiber-reinforced resin composite material can be obtained by impregnating a reinforcing fiber substrate with a liquid resin (i.e., for example, an uncured curable resin or a molten thermoplastic resin) and curing or solidifying it.

[0083] There are no particular limitations on the method for producing the fiber-reinforced composite material. A prepreg may be formed by pre-impregnating a reinforcing fiber substrate with a matrix resin, or the reinforcing fiber substrate and matrix resin may be composited simultaneously with molding by resin transfer molding (RTM) or resin film infusion molding (RFI). Preferably, the reinforcing fiber substrate of the present invention is used in molding methods such as RTM or RFI.

[0084] (Matrix resin) The matrix resin that can be used in the present invention is a thermosetting resin or a thermoplastic resin. The coefficient of linear expansion (CTEm) of the matrix resin is preferably 40 × 10⁻⁶. -6 ~70×10 -6 The matrix resin is / K. The matrix resin may be a mixture of one or more resins, and may also contain colorants, fillers, various additives, etc. If the matrix resin contains a thermosetting resin, the amount of the thermosetting resin may be 30% by mass or more, 40% by mass or more, or 50% by mass or more relative to the matrix resin, and / or 100% by mass or less, 90% by mass or less, 80% by mass or less, or 70% by mass or less.

[0085] Examples of thermosetting resins include epoxy resins, unsaturated polyester resins, phenolic resins, melamine resins, polyurethane resins, silicone resins, maleimide resins, vinyl ester resins, cyanate ester resins, resins obtained by prepolymerizing maleimide resin and cyanate ester resin, urethane acrylate resins, phenoxy resins, alkyd resins, urethane resins, bismaleimide resins, polyimide resins and polyisoimide resins having acetylene ends, and polyimide resins having nadic acid ends. These can be used individually or as mixtures of two or more. Among these, epoxy resins, vinyl ester resins, bismaleimide resins, and polyimide resins, which have excellent heat resistance, elastic modulus, and chemical resistance, are particularly preferred.

[0086] (Epoxy resin) The epoxy resins that can be used as thermosetting resins in the present invention are not particularly limited, but include tetrafunctional glycidylamine type epoxy resins such as tetraglycidyl-4,4'-diaminodiphenylmethane, tetraglycidyl-4,4'-diaminodiphenyl sulfone, tetraglycidyl-3,3'-diaminodiphenyl sulfone, tetraglycidyl-4,4'-diaminodiphenyl ether, and tetraglycidyl-3,4'-diaminodiphenyl ether, as well as trifunctional epoxy resins such as triglycidyl-m-aminophenol, triglycidyl-p-aminophenol, and triglycidyl isocyanurate. Examples include lipids, diglycidylaniline and its derivatives such as diglycidyl-o-toluidine, diglycidyl-m-toluidine, diglycidyl-p-toluidine, diglycidyl-xylidine, diglycidyl-mesidine, diglycidyl-anisidine, diglycidyl-phenoxyaniline, or diglycidyl-naphthylamine and its derivatives, bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, bisphenol S diglycidyl ether, resorcinol diglycidyl ether, and 1,6-naphthalenediol diglycidyl ether, as well as other bifunctional epoxy resins. These epoxy resins may be used individually or in combination.

[0087] (Hardening agent) In the present invention, known curing agents can be used with the thermosetting resin. In particular, the use of amine-based curing agents is preferred from the viewpoint of the mechanical properties of the cured product. The thermosetting resin used in the present invention may or may not contain this curing agent beforehand. Thermosetting resins that do not contain a curing agent are made in a state that can be mixed with a curing agent before or during curing.

[0088] Examples of amine-based curing agents include latent curing agents such as dicyandiamide, aliphatic polyamines, various isomers of aromatic polyamine curing agents, aminobenzoic acid esters, and acid anhydrides. Dicyandiamide is preferred because it provides excellent storage stability for reinforced fiber substrates impregnated with matrix resin.

[0089] Aliphatic polyamines are preferred because they are highly reactive and allow for curing reactions at low temperatures. Examples of aliphatic polyamines include 4,4'-diaminodicyclohexylmethane, isophoronediamine, and m-xylylenediamine.

[0090] Aromatic polyamines are preferred because they have excellent heat resistance and various mechanical properties. Examples of aromatic polyamines include diaminodiphenylsulfone, diaminodiphenylmethane, and toluenediamine derivatives. Aromatic diamine compounds such as 4,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfone, and 4,4'-diaminodiphenylmethane, and derivatives thereof having non-reactive substituents, are particularly preferred from the viewpoint of providing a cured product with good heat resistance. Here, the non-reactive substituents are the same as those described in the description of epoxy resins.

[0091] Preferably, trimethylene glycol di-p-aminobenzoate and neopentyl glycol di-p-aminobenzoate are used as aminobenzoic acid esters. Composite materials cured using these have inferior heat resistance compared to various isomers of diaminodiphenylsulfone, but they have excellent tensile elongation.

[0092] Examples of acid anhydrides include 1,2,3,6-tetrahydrophthalic anhydride, hexahydrophthalic anhydride, and 4-methylhexahydrophthalic anhydride. When these curing agents are used, the pot life of the uncured resin composition is long, and a cured product with a relatively balanced electrical, chemical, and mechanical property is obtained. Therefore, the type of curing agent used is appropriately selected depending on the application of the composite material.

[0093] Furthermore, when using thermosetting resins in the RTM molding method, it is preferable to include a curing agent comprising an aromatic polyamine, wherein the aromatic polyamine has at least one substituent of an aliphatic substituent, an aromatic substituent, or a halogen atom at the ortho position relative to the amino group.

[0094] Suitable curing agents for the RTM molding method include any polyamine having the structure described above, but specific examples include 4,4'-diaminodiphenylmethane and its derivatives, phenylenediamine and its derivatives.

[0095] Examples of derivatives of 4,4'-diaminodiphenylmethane include hindered amine compounds such as 4,4'-methylenebis(2,6-diethylaniline), 4,4'-methylenebis(2-ethyl-6-methylaniline), and 4,4'-methylenebis(2-isopropyl-6-methylaniline). These curing agents can improve the storage stability of uncured thermosetting resins, the pot life during RTM molding, and the water absorption properties of cured resins.

[0096] Examples of phenylenediamine derivatives include 2,4-diaminotoluene, 2,6-diaminotoluene, 2,4,6-trimethyl-1,3-phenylenediamine, m-phenylenediamine, diethyltoluenediamine, and dimethylthiotoluenediamine. These curing agents can improve the curing speed of uncured thermosetting resins and viscosity characteristics during RTM molding, as well as improve the mechanical properties and heat resistance of cured resin products.

[0097] The total amount of curing agent contained in the thermosetting resin that can be used in the present invention is an amount suitable for curing all thermosetting resins (especially all epoxy compounds) blended in the matrix resin, and is appropriately adjusted depending on the type of thermosetting resin (especially epoxy compound) and curing agent used.

[0098] Specifically, for example, the ratio of the number of epoxy groups in the epoxy compound in the matrix resin to the number of active hydrogens in the curing agent is preferably 0.7 to 1.3, more preferably 0.8 to 1.2, and particularly preferably 0.9 to 1.1. If this ratio is less than 0.7 or greater than 1.3, the molar balance between epoxy groups and active hydrogens will be disrupted, which may result in insufficient crosslinking density in the resulting cured resin, and may lead to reduced heat resistance and mechanical properties such as elastic modulus and fracture toughness.

[0099] If the matrix resin contains a thermosetting resin, it may also contain colorants, fillers, various additives, etc., in addition to curing agents and curing accelerators. To improve the impact resistance of the matrix resin, it is preferable that it contains thermoplastic resin components or resin particles.

[0100] (Thermoplastic resin component) The matrix resin may further contain a thermoplastic resin in addition to the thermosetting resin. Examples of thermoplastic resins include epoxy-soluble thermoplastic resins and epoxy-insoluble thermoplastic resins.

[0101] The epoxy-soluble thermoplastic resin adjusts the viscosity of the matrix resin and improves the impact resistance of the resulting fiber-reinforced composite material. This epoxy-soluble thermoplastic resin is a thermoplastic resin that can be partially or completely dissolved in the epoxy resin at or below the temperature at which the fiber-reinforced composite material is molded.

[0102] Here, partial dissolution in the epoxy resin means that when 10 parts by mass of a thermoplastic resin with an average particle size of 20-50 μm is mixed with 100 parts by mass of epoxy resin and stirred at 190°C for 1 hour, the particles disappear or the particle size (particle diameter) changes by 10% or more.

[0103] On the other hand, epoxy resin-insoluble thermoplastic resin refers to a thermoplastic resin that does not substantially dissolve in epoxy resin at or below the temperature at which fiber-reinforced composite materials are molded. In other words, it refers to a thermoplastic resin in which, when 10 parts by mass of a thermoplastic resin with an average particle size of 20 to 50 μm is mixed with 100 parts by mass of epoxy resin and stirred at 190°C for 1 hour, the particle size does not change by more than 10%. Generally, the temperature at which fiber-reinforced composite materials are molded is 100 to 190°C. Furthermore, particle size is measured visually using a microscope, and the average particle size refers to the average value of the particle sizes of 100 randomly selected particles.

[0104] If the epoxy resin-soluble thermoplastic resin is not completely dissolved, heating during the epoxy resin curing process can dissolve it in the epoxy resin, increasing the viscosity of the matrix resin. This prevents matrix resin flow (the phenomenon of matrix resin leaking out from the reinforcing fiber substrate impregnated with matrix resin) caused by viscosity reduction during the curing process.

[0105] The epoxy resin-soluble thermoplastic resin is preferably one that dissolves in epoxy resin at 190°C in an amount of 80% by mass or more.

[0106] Specific examples of epoxy resin-soluble thermoplastic resins include polyethersulfone, polysulfone, polyetherimide, and polycarbonate. These may be used individually or in combination of two or more. The epoxy resin-soluble thermoplastic resin included in the epoxy resin composition is particularly preferably polyethersulfone or polysulfone with a weight-average molecular weight (Mw) in the range of 8,000 to 100,000, as measured by gel permeation chromatography. If the weight-average molecular weight (Mw) is less than 8,000, the impact resistance of the resulting fiber-reinforced composite material will be insufficient, and if it is greater than 100,000, the viscosity may become significantly higher, resulting in significantly poor handling.

[0107] The molecular weight distribution of the epoxy resin-soluble thermoplastic resin is preferably uniform. In particular, the polydispersity (Mw / Mn), which is the ratio of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn), is preferably in the range of 1 to 10, and more preferably in the range of 1.1 to 5.

[0108] Epoxy resin-soluble thermoplastic resins preferably have reactive groups that are reactive with the epoxy resin or functional groups that form hydrogen bonds. Such epoxy resin-soluble thermoplastic resins can improve the dissolution stability during the curing process of the epoxy resin. Furthermore, they can impart toughness, chemical resistance, heat resistance, and moisture heat resistance to the resulting fiber-reinforced composite material after curing.

[0109] Preferred reactive groups that react with epoxy resins are hydroxyl groups, carboxylic acid groups, imino groups, and amino groups. Using polyethersulfones with hydroxyl group termini is more preferable because the resulting fiber-reinforced composite material exhibits particularly excellent impact resistance, fracture toughness, and solvent resistance.

[0110] The content of epoxy resin-soluble thermoplastic resin in the matrix resin is adjusted as appropriate according to the viscosity. From the viewpoint of processability of the prepreg and / or fiber-reinforced composite material, the content of epoxy resin-soluble thermoplastic resin in the matrix resin is preferably 5 to 90 parts by mass, more preferably 5 to 40 parts by mass, and particularly preferably 15 to 35 parts by mass per 100 parts by mass of epoxy resin. If it is less than 5 parts by mass, the impact resistance of the resulting fiber-reinforced composite material may be insufficient, which is undesirable. On the other hand, if the content of epoxy resin-soluble thermoplastic resin exceeds 90 parts by mass, the viscosity becomes significantly higher, and the handling of the reinforced fiber substrate impregnated with the matrix resin may deteriorate significantly, which is undesirable.

[0111] Epoxy resin-soluble thermoplastic resins preferably contain reactive aromatic oligomers having amine-terminated groups (hereinafter also simply referred to as "aromatic oligomers").

[0112] During heat curing, the matrix resin undergoes a high molecular weight increase due to the curing reaction between the epoxy resin and the curing agent. This increase in molecular weight expands the two-phase region, causing the aromatic oligomers dissolved in the matrix resin to undergo reaction-induced phase separation. This phase separation forms a two-phase structure within the matrix resin where the cured epoxy resin and aromatic oligomers co-continuously exist. Furthermore, since the aromatic oligomers have amine-terminated groups, they also react with the epoxy resin. Because each phase in this co-continuous two-phase structure is strongly bonded to each other, solvent resistance is also improved.

[0113] This co-continuous structure absorbs external impacts to the fiber-reinforced composite material, suppressing crack propagation. As a result, fiber-reinforced composite materials made using reactive aromatic oligomers with amine-terminated groups exhibit high impact resistance and fracture toughness.

[0114] As the aromatic oligomer, known polysulfones having amine-terminated groups and polyethersulfones having amine-terminated groups can be used. The amine-terminated group is preferably a primary amine (-NH2)-terminated group.

[0115] The aromatic oligomer incorporated into the matrix resin preferably has a weight-average molecular weight of 8,000 to 40,000, as measured by gel permeation chromatography. A weight-average molecular weight of less than 8,000 is undesirable because it reduces the toughness-improving effect of the matrix resin. On the other hand, a weight-average molecular weight exceeding 40,000 is also undesirable because it increases the viscosity of the matrix resin, making it difficult for the resin composition to penetrate the reinforcing fiber layer and thus increasing processing problems.

[0116] As aromatic oligomers, commercially available products such as "Virantage DAMS VW-30500 RP (registered trademark)" (manufactured by Solvay Specialty Polymers) can be preferably used.

[0117] The epoxy resin-soluble thermoplastic resin is preferably in particulate form. Particulate epoxy resin-soluble thermoplastic resin can be uniformly blended into the matrix resin. Furthermore, the resulting prepreg and / or fiber-reinforced composite material has high moldability.

[0118] The average particle size of the epoxy resin-soluble thermoplastic resin is preferably 1 to 50 μm, and more preferably 3 to 30 μm. If it is less than 1 μm, the viscosity of the matrix resin increases significantly, making it difficult to add a sufficient amount of epoxy resin-soluble thermoplastic resin to the matrix resin, which is undesirable. On the other hand, if it exceeds 50 μm, it may be difficult to obtain a sheet of uniform thickness when processing the matrix resin into a sheet, and the dissolution rate in the epoxy resin slows down, resulting in an uneven fiber-reinforced composite material, which is also undesirable.

[0119] When the matrix resin contains a thermosetting resin, the matrix resin may contain not only an epoxy-soluble thermoplastic resin but also an epoxy-insoluble thermoplastic resin. Some of the epoxy-insoluble thermoplastic resin and the epoxy-soluble thermoplastic resin (epoxy-soluble thermoplastic resin that remains undissolved in the matrix resin after curing) become dispersed particles within the matrix resin of the fiber-reinforced composite material (hereinafter, these dispersed particles are also referred to as "interlayer particles"). These interlayer particles suppress the propagation of impacts received by the fiber-reinforced composite material. As a result, the impact resistance of the resulting fiber-reinforced composite material is improved.

[0120] Examples of epoxy resin-insoluble thermoplastic resins include polyamide, polyacetal, polyphenylene oxide, polyphenylene sulfide, polyester, polyamide-imide, polyimide, polyether ketone, polyether ether ketone, polyethylene naphthalate, polyether nitrile, and polybenzimidazole. Among these, polyamide, polyamide-imide, and polyimide are preferred due to their high toughness and heat resistance. Polyamides and polyimides exhibit particularly excellent toughness-enhancing effects on fiber-reinforced composite materials. These can be used individually or in combination of two or more. Copolymers of these materials can also be used.

[0121] In particular, the heat resistance of the resulting fiber-reinforced composite material can be especially improved by using amorphous polyimides, or polyamides such as Nylon 6 (registered trademark) (a polyamide obtained by the ring-opening polycondensation reaction of caprolactam), Nylon 11 (a polyamide obtained by the ring-opening polycondensation reaction of undecanelactam), Nylon 12 (a polyamide obtained by the ring-opening polycondensation reaction of lauryllactam), Nylon 1010 (a polyamide obtained by the copolymerization reaction of sebaciac acid and 1,10-decanediamine), or amorphous nylon (also called transparent nylon, which is nylon in which polymer crystallization does not occur or the rate of polymer crystallization is extremely slow).

[0122] The content of epoxy resin-insoluble thermoplastic resin in the matrix resin that can be used in the present invention is appropriately adjusted according to the viscosity of the matrix resin. From the viewpoint of processability of the prepreg and / or fiber-reinforced composite material, the content is preferably 5 to 50 parts by mass, more preferably 10 to 45 parts by mass, and particularly preferably 20 to 40 parts by mass, per 100 parts by mass of epoxy resin contained in the matrix resin. If it is less than 5 parts by mass, the impact resistance of the resulting fiber-reinforced composite material may be insufficient, which is undesirable. On the other hand, if it exceeds 50 parts by mass, it may reduce the impregnation of the matrix resin and the drape of the reinforced fiber substrate impregnated with the matrix resin, which is undesirable.

[0123] The preferred average particle size and morphology of epoxy-insoluble thermoplastic resins are similar to those of epoxy-soluble thermoplastic resins.

[0124] (Resin particles) If the matrix resin used in the present invention includes a thermosetting resin, the matrix resin may further contain resin particles. The resin particles exist dispersed in the thermosetting resin (particularly epoxy resin) without dissolving, and also exist in a dispersed state in the cured resin after the thermosetting resin (particularly epoxy resin) has hardened. When the cured resin is considered as a sea component, the resin particles exist in the cured resin as island components.

[0125] The inclusion of resin particles is preferable because it allows for high fracture toughness and impact resistance in cured resin products and fiber-reinforced composite materials. Furthermore, the inclusion of resin particles in the matrix resin can result in particularly good microcrack resistance.

[0126] As resin particles, for example, thermoplastic resin particles, thermosetting resin particles, and rubber particles can be used, and rubber particles are preferred. Examples of rubber particles include silicone rubber, butadiene rubber, styrene-butadiene rubber, and methyl-butadiene-styrene methacrylate rubber. One type of resin particle may be used alone, or two or more types may be used in combination.

[0127] Commercially available rubber particles for use as resin particles include MX-153 (33% by mass of butadiene rubber single dispersion in bisphenol A type epoxy resin, manufactured by Kaneka Corporation), MX-257 (37% by mass of butadiene rubber single dispersion in bisphenol A type epoxy resin, manufactured by Kaneka Corporation), MX-154 (40% by mass of butadiene rubber single dispersion in bisphenol A type epoxy resin, manufactured by Kaneka Corporation), MX-960 (25% by mass of silicone rubber single dispersion in bisphenol A type epoxy resin, manufactured by Kaneka Corporation), MX-136 (25% by mass of butadiene rubber single dispersion in bisphenol F type epoxy resin, manufactured by Kaneka Corporation), and MX-965 (25% by mass of silicone rubber single dispersion in bisphenol F type epoxy resin). Examples include: MX-217 (a single dispersion of butadiene rubber in a phenol novolac type epoxy resin, manufactured by Kaneka Corporation), MX-227M75 (a single dispersion of styrene butadiene rubber in a bisphenol A novolac type epoxy resin, manufactured by Kaneka Corporation), MX-334M75 (a single dispersion of styrene butadiene rubber in a brominated epoxy resin, manufactured by Kaneka Corporation), MX-414 (a single dispersion of butadiene rubber in a tetrafunctional glycidylamine type epoxy resin, manufactured by Kaneka Corporation), and MX-451 (a single dispersion of styrene butadiene rubber in a trifunctional glycidylamine type epoxy resin, manufactured by Kaneka Corporation).

[0128] The average particle size of the resin particles is preferably 1.0 μm or less, more preferably 0.5 μm or less, and particularly preferably 0.3 μm or less. The average particle size is preferably 0.03 μm or more, more preferably 0.05 μm or more, and particularly preferably 0.08 μm or more. An average particle size of 1.0 μm or less is preferable because, in the matrix resin impregnation process into the fiber-reinforced substrate, the resin particles are not filtered out on the surface of the fiber-reinforced substrate, making it easy to impregnate the inside of the reinforcing fiber bundle. This prevents poor resin impregnation and allows for the production of a fiber-reinforced composite material with excellent physical properties.

[0129] The average particle size of resin particles can be determined by observing a cross-section of the fiber-reinforced composite material with a scanning electron microscope or transmission electron microscope, measuring the diameter of at least 50 resin particles, and averaging them. The observation can be performed at 25,000x magnification. If the resin particles are not perfectly round, i.e., if they are elliptical or otherwise, the maximum diameter of the resin particle can be used as the particle size of that resin particle.

[0130] The content of resin particles is preferably 0.1 to 30 parts by mass, more preferably 0.5 to 20 parts by mass, and particularly preferably 1 to 10 parts by mass, based on 100 parts by mass of total thermosetting resin (especially 100 parts by mass of total epoxy resin). A content of 0.1 parts by mass or more is preferable because it can sufficiently improve the fracture toughness and impact resistance of the cured resin and fiber composite material. On the other hand, a content of 30 parts by mass or less is preferable because it can lower the viscosity of the matrix resin and improve impregnation into the fiber substrate.

[0131] The resin particles can also be used as a masterbatch in which they are dispersed at a high concentration in a thermosetting resin (especially epoxy resin). In this case, it becomes easier to highly disperse the resin particles in the thermosetting resin (especially epoxy resin).

[0132] In one embodiment of the present disclosure, the matrix resin constituting the fiber-reinforced composite material contains 0.1 to 30 parts by mass of resin particles per 100 parts by mass of thermosetting resin, and these resin particles have an average particle diameter of 1.0 μm or less.

[0133] (RTM method) The fiber-reinforced composite material of the present invention is preferably obtained by the RTM (Resin Transfer Molding) method, from the viewpoint of efficiently obtaining fiber-reinforced composite materials with complex shapes. The RTM method includes the steps of impregnating a reinforcing fiber substrate placed in a mold with a liquid thermosetting resin or molten thermoplastic resin as a matrix resin, and curing or solidifying the matrix resin to obtain a fiber-reinforced composite material.

[0134] In the present invention, the mold used in the RTM method may be a closed mold made of a rigid material, or it may be an open mold made of a rigid material and a flexible film (bag). In the latter case, the reinforcing fiber substrate can be placed between the open mold made of the rigid material and the flexible film. Various existing materials can be used as the rigid material, such as metals such as steel and aluminum, fiber-reinforced plastics (FRP), wood, and gypsum. Materials that can be used for the flexible film include polyamide, polyimide, polyester, fluororesin, and silicone resin.

[0135] In the RTM (Return to Molding) method, when using a closed mold made of rigid material, it is common practice to pressurize the mold and then pressurize the matrix resin before injecting it. In this case, it is also possible to provide a suction port in addition to the injection port and connect it to a vacuum pump for suction. By using suction, it is possible to inject the matrix resin using only atmospheric pressure without the need for special pressurizing means. This method is suitable because it allows for the manufacture of large components by providing multiple suction ports.

[0136] In the RTM method, when using an open mold of a rigid material and a flexible film, the matrix resin may be injected using only atmospheric pressure by suction, without the use of any special pressurizing means. To achieve good impregnation with injection using only atmospheric pressure, it is effective to use a resin diffusion medium. Furthermore, it is preferable to apply a gel coat to the surface of the rigid material prior to the installation of the reinforcing fiber substrate.

[0137] In the RTM method, when a thermosetting resin is used as the matrix resin, the matrix resin is impregnated into the reinforcing fiber substrate, and then heat curing is performed. The mold temperature during heat curing is usually selected to be higher than the mold temperature when the thermosetting resin is injected. The mold temperature during heat curing is preferably 80 to 200°C. The heat curing time is preferably 1 minute to 20 hours. After heat curing is complete, the mold is demolded and the fiber-reinforced composite material is removed. After that, the obtained fiber-reinforced composite material may be heated at a higher temperature for post-curing. The post-curing temperature is preferably 150 to 200°C, and the time is preferably 1 minute to 4 hours.

[0138] Impregnation of a reinforcing fiber substrate with a matrix resin can be performed, for example, by injecting a matrix resin containing a thermosetting resin heated (for example, in the range of 80 to 120°C) into a vacuum system containing the reinforcing fiber substrate. Specifically, for example, a hose for forming a resin injection port and a resin discharge port is placed, the reinforcing fiber substrate is covered with a bag (for example, a nylon bag film), and sealed with sealant tape or the like. Then, after reducing the pressure inside the bag (for example, to 5 Torr or less), impregnation can be performed by injecting a matrix resin containing a thermosetting resin heated (for example, in the range of 80 to 120°C) through the resin injection port.

[0139] When epoxy resin is used as the matrix resin, the impregnation pressure when impregnating the reinforcing fiber substrate with epoxy resin using the RTM method is determined appropriately, taking into account the viscosity and resin flow of the resin. The specific impregnation pressure is 0.001 to 10 MPa, and preferably 0.01 to 1 MPa. When obtaining fiber-reinforced composite materials using the RTM method, the viscosity of the epoxy resin at 100°C is preferably less than 5000 mPa·s, and more preferably 1 to 1000 mPa·s.

[0140] The amount of matrix resin is preferably 20 to 60 parts by mass, and more preferably 30 to 40 parts by mass, per 100 parts by mass of the reinforcing fiber base material.

[0141] In this molding method, the viscosity of the matrix resin is preferably 0.01 to 1 Pa·s at the injection temperature. It is preferable to pre-treat the resin to be injected by heating or other methods to adjust its viscosity to the above range at the time of injection.

[0142] (Microcracks) The fiber-reinforced composite material according to this disclosure has a reinforcing fiber base material according to this disclosure, and therefore the crack density is reduced. Specifically, the crack density after the thermal shock test is preferably 0.30 cracks / (cm·ply) or less, more preferably 0.20 cracks / (cm·ply) or less, and even more preferably 0.10 cracks / (cm·ply) or less.

[0143] The thermal shock test, used to measure crack density after a thermal shock test, can be performed as follows: A thermal shock testing machine is used to subject a fiber-reinforced composite material to 1000 thermal cycles. Each thermal cycle is set to consist of a 15-minute flat zone at 55°C, followed by a 15-minute temperature change zone reaching 70°C, followed by a 15-minute flat zone at 70°C, and then a 15-minute temperature change zone returning to -55°C. This cycle is repeated 1000 times.

[0144] The crack density after thermal shock testing can be measured as follows: The number of cracks in the cross-section of the fiber-reinforced resin composite material specimen after the thermal shock test described above is measured by microscopic observation at 200x magnification. More specifically, the specimen (80mm wide x 50mm long x 5mm thick) after the thermal shock test is cut into four equal parts of 40mm wide x 25mm long, the cut surfaces in the thickness direction are mirror-polished, and the long and short sides are used as observation surfaces. The observation range for microcracks under microscopic observation is 50mm. 2 The crack density is calculated by dividing the number of measured cracks by the number of layers and the width of the observation surface. The unit of crack density is cracks / (cm·ply). The crack density values ​​obtained from observations of the long and short sides are averaged to obtain the final crack density.

[0145] <Application> Applications of the reinforced fiber substrate and fiber-reinforced resin composite materials (composites) manufactured using the same as described herein include, for example, structural materials for aircraft, automobiles, railway vehicles, and ships. In other words, the reinforced fiber substrate and composite materials manufactured using the same as described herein can be used as materials constituting the bodies of aircraft, automobiles, railway vehicles, and ships. [Examples]

[0146] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The components and test methods used in the examples and comparative examples are described below.

[0147] <Evaluation Method> The evaluations performed in the examples and comparative examples were carried out as follows.

[0148] (Coefficient of thermal expansion of auxiliary thread) The fiber sample was heated at 180°C for 2 hours without applying tension, then naturally cooled in 25°C air. After that, the coefficient of linear expansion in the direction of the fiber axis was measured using a thermomechanical analyzer (TA Instruments, Model: TMA Q400). [Measurement conditions] Temperature at which heating begins: -60℃ Measurement temperature range: -50 to 70°C End temperature for heating: 100℃ Heating rate: 5°C / min Load: 0.0001N

[0149] (Melting point of auxiliary thread) The melting point of the auxiliary thread was measured according to JIS K7121. A 3 mg sample of auxiliary thread was weighed into an aluminum pan. The melting point of the auxiliary thread was measured using a DSC (NETZSCH DSC3500 Sirius) at the peak of the fusion endothermic peak. If there were multiple fusion endothermic peaks, the lowest temperature value measured was used as the melting point of the auxiliary thread. [Measurement conditions] Measurement temperature range: Room temperature to 250°C Heating rate: 5°C / min

[0150] (Melting point of nonwoven fabric) The melting point of the thermoplastic resin fibers constituting the nonwoven fabric was measured according to JIS K7121. A 3 mg sample of nonwoven fabric was weighed into an aluminum pan. The melting point of the nonwoven fabric was measured using a DSC (NETZSCH DSC3500 Sirius) at the peak of the melting endothermic peak. If there were multiple melting endothermic peaks, the lowest temperature value was used as the melting point of the nonwoven fabric. [Measurement conditions] Measurement temperature range: Room temperature to 250°C Heating rate: 5°C / min

[0151] (Average fiber diameter of thermoplastic resin fibers) The average fiber diameter of the thermoplastic resin fibers constituting the nonwoven fabric as a resin material layer was measured by averaging the fiber diameter values ​​measured for at least 30 fibers using an optical microscope. A Keyence VHX-5000 microscope was used, and observations were performed at 300x magnification.

[0152] (Coefficient of variation of fiber diameter) The coefficient of variation of the fiber diameter of the thermoplastic resin fibers constituting the nonwoven fabric was determined by dividing the standard deviation of the fiber diameters measured for at least 30 fibers using an optical microscope by the average fiber diameter. A Keyence VHX-5000 microscope was used, and observations were performed at 300x magnification.

[0153] (Fiber fineness, number of single fibers) The stitching thread, used as an auxiliary thread, was wound 100m using a measuring machine, and its mass was measured. The mass obtained was multiplied by 100 to calculate the mass per 10,000m, and this value was defined as the fineness (dtex). The number of single threads in the stitching thread was measured by observation using an optical microscope.

[0154] (Cold and thermal shock test) A thermal shock tester (TSA-73EH-W, manufactured by ESPEC Corporation) was used to subject a fiber-reinforced composite material to 1000 thermal cycles. Each thermal cycle was set to consist of a 15-minute flat period at -55°C, followed by a 15-minute temperature change period reaching 70°C, followed by a 15-minute flat period at 70°C, and then a 15-minute temperature change period returning to -55°C. This cycle was repeated 1000 times.

[0155] (crack density) The number of cracks in the cross-section of fiber-reinforced composite material specimens after thermal shock testing was measured by microscopic observation. A Keyence VHX-5000 microscope was used, and observations were performed at 200x magnification. Specifically, the specimen (80mm wide x 50mm long x 5mm thick) after thermal shock testing was cut into four equal sections of 40mm wide x 25mm long. The cut surfaces in the thickness direction were mirror-polished, and the long and short sides were used as observation surfaces. The observation range for microcracks during microscopic observation was 50mm. 2 The crack density was calculated by dividing the number of measured cracks by the number of layers (ply) and the width of the observation surface (L (cm)). The unit of crack density is cracks / (cm·ply). The crack density values ​​obtained from observations of the long and short sides were averaged to obtain the final crack density.

[0156] (Post-impact compressive strength (CAI compressive strength)) Carbon fiber reinforced polymer (CFRP) was cut to dimensions of 101.6 mm in width and 152.4 mm in length to obtain test specimens for post-impact compression (CAI) testing. Using these test specimens, an impact of 30.5 J was applied to cause damage according to SACMA SRM 2R-94, and the post-impact compressive strength (in MPa) was measured. The crosshead speed of the specimen compression testing machine was set to 1 mm / min, and measurements were performed on five test specimens.

[0157] (Method for measuring the average particle size of resin particles contained in the matrix resin) The cross-section of the heat-cured fiber-reinforced composite material was observed at 25,000x magnification using a scanning electron microscope or transmission electron microscope. The diameters of at least 50 particles were measured and the average particle diameter was determined by averaging them. If a particle was not perfectly circular, i.e., elliptical, the maximum diameter of that particle was used as its particle diameter.

[0158] <Components> The components used in the examples and comparative examples are as follows.

[0159] (Reinforced fiber) The following carbon fiber bundles were used as reinforcing fibers: Carbon fiber bundle "Tenax®" (manufactured by Teijin Limited, product number: HTS45-12K, tensile strength 4.5 GPa, tensile modulus 240 GPa, coefficient of linear expansion -0.5 × 10⁻⁶) -6 / K)

[0160] (unidirectional fabric) • Unidirectional Woven Fabric S-1: Manufactured by TEIJIN CARBON EUROPE GmbH. Dry Reinforcements Woven Fabric DRWF HTS45-UD. Reinforced fiber HTS45-12K. Reinforced fiber weight 194g / m². 2

[0161] This reinforced fiber base material (unidirectional fabric S-1) is a fabric composed of the above-mentioned carbon fiber bundle HTS45-12K as the warp threads, which are aligned in one direction, and the following auxiliary threads as the weft threads, and is a so-called bamboo blind fabric. • Weft auxiliary yarn (weft): EMS-CHEMIE AG's Grilon (registered trademark) K-85, a composite fiber of polyamide resin and polyester resin, fineness 200 dtex, 44 single filaments, *The coefficient of linear expansion cannot be measured as it melts when heated at 180°C for 2 hours, melting point 86°C

[0162] (Support thread) For the auxiliary stitching thread, one of the following stitching threads was used. • Stitching thread A-1: ​​JOINER (registered trademark) H-Type, manufactured by Fuji Spinning Holdings Co., Ltd., copolymer polyamide resin fiber, fineness 33 dtex, 5 strands per filament, *The coefficient of linear expansion cannot be measured as it melts when heated at 180°C for 2 hours, melting point 131°C • Stitching thread A-2: EMS-CHEMIE AG Grilon (registered trademark) KE-160, polyester resin fiber, fineness 75 dtex, 14 strands per filament, *Measuring coefficient of linear expansion is not possible as it melts upon heating at 180°C for 2 hours, melting point 159°C • Stitching thread A-3: Asahi Kasei Corporation, Bemberg® (registered trademark), copper ammonia rayon fiber (cellulose fiber), fineness 33 dtex, 24 strands per filament, coefficient of thermal expansion 12 × 10⁻¹⁰ -6 / K, no melting point *thermal decomposition occurs above 200℃ • Stitching thread A-4: EMS-CHEMIE AG Grilon (registered trademark) K-178, polyamide resin fiber (PA12), fineness 23 dtex, 4 strands of single yarn, coefficient of thermal expansion 70 × 10 -6 / K, melting point 177℃ • Stitching thread A-5: EMS-CHEMIE AG Grilon (registered trademark) K-203, polyamide resin fiber (PA6 / PA12 copolymer), fineness 33 dtex, 8 strands of single filament, coefficient of thermal expansion 30 × 10⁻¹⁰ -6 / K, melting point 194℃ • Stitching thread A-6: Manufactured by KB Seiren Co., Ltd., 33T-12-SOD0, polyester resin fiber, fineness 33 dtex, 12 strands of single yarn, coefficient of thermal expansion 100 × 10 -6 / K, melting point 257℃ • Stitching thread A-7: EMS-CHEMIE AG Grilon (registered trademark) K-178, polyamide resin fiber (PA12), fineness 33 dtex, 6 strands of single yarn, coefficient of thermal expansion 70 × 10 -6 / K, melting point 177℃

[0163] (Oil treatment agent) • Oil 1: Aliphatic epoxy compound "Denacol" (registered trademark) EX832 (polyoxyethylene diglycidyl ether manufactured by Nagase ChemteX Corporation, number of epoxy groups: 2, epoxy equivalent: 284 g / Eq) 5 wt% aqueous solution (mixed so that the weight ratio of polyoxyethylene diglycidyl ether to water is 1:19)

[0164] (Matrix resin) An epoxy resin, a liquid thermosetting resin, was used as the matrix resin for the fiber-reinforced resin composite material. Its composition (C-1 and C-2) is as follows. The coefficient of linear expansion of the cured product is 59 × 10⁻⁶ for both. -6 It was / K.

[0165] • Matrix resin C-1: (Epoxy resin) Tetraglycidyl-4,4'-diaminodiphenylmethane (Araldite® MY721, manufactured by Huntsman Japan Co., Ltd.) 56 parts by mass • N,N-Diglycidylaniline (GAN (product name), manufactured by Nippon Kayaku Co., Ltd.) 30 parts by mass (resin particle component) • MX-414 (Manufactured by Kaneka Corporation, MX-414 (product name), average particle size 0.11 μm, masterbatch prepared by dispersing particulate polybutadiene rubber components in a glycidylamine-type tetrafunctional epoxy resin at a concentration of 25% by mass) 19 parts by mass (Hardening agent) 4,4'-Diamino-3,3'-Diisopropyl-5,5'-Dimethyldiphenylmethane (Lonzacure® M-MIPA d, manufactured by Arcsarda Japan Co., Ltd.) 31 parts by mass • Diethyltoluenediamine (Lonzacure® DETDA80, manufactured by Arcsada Japan Co., Ltd.) 21 parts by mass

[0166] Matrix resin C-2: (Epoxy resin) • Tetraglycidyl-4,4'-diaminodiphenylmethane (Araldite® MY721, manufactured by Huntsman Japan Co., Ltd.) 70 parts by mass • N,N-Diglycidylaniline (GAN (product name), manufactured by Nippon Kayaku Co., Ltd.) 30 parts by mass (Hardening agent) 4,4'-Diamino-3,3'-Diisopropyl-5,5'-Dimethyldiphenylmethane (Lonzacure® M-MIPA d, manufactured by Arcsarda Japan Co., Ltd.) 31 parts by mass • Diethyltoluenediamine (Lonzacure® DETDA80, manufactured by Arcsada Japan Co., Ltd.) 21 parts by mass

[0167] (Raw materials for the resin material layer) • Polyamide PA12, melting point 178℃, manufactured by Daicel-Evonik Corporation (product name: Diamide L1640) • Polyamide PA6-10, melting point 222℃, manufactured by Daicel-Evonik Corporation (product name: Vestamid TERRA HS16) • Polyamide PA6-12, melting point 215℃, manufactured by Daicel-Evonik Corporation (product name: Vestamid DX9308) • Polyamide PA10-10, melting point 199°C, manufactured by Daicel-Evonik Corporation (product name: Vestamid TERRA DS16) • Polyamide PA6 / PA12 copolymer, melting point 197°C, manufactured by EMS-CHEMIE (product name Grilon K-203)

[0168] (Resin material layer) As the resin material layer, the following nonwoven fabric was used, which was manufactured by the melt-blown method using the above-mentioned resin raw materials. Nonwoven fabric B-1: Polyamide PA12, average fiber diameter 5.8 μm (coefficient of variation of fiber diameter: 0.13), basis weight 5 g / m² 2 Nonwoven fabric B-2: Polyamide PA12, average fiber diameter 16.3 μm (coefficient of variation of fiber diameter: 0.09), basis weight 5 g / m² 2 Nonwoven fabric B-3: Polyamide PA12, average fiber diameter 29.3 μm (coefficient of variation of fiber diameter: 0.08), basis weight 5 g / m² 2 Nonwoven fabric B-4: Polyamide PA12, average fiber diameter 5.7 μm (coefficient of variation of fiber diameter: 0.14), basis weight 3 g / m² 2 Nonwoven fabric B-5: Polyamide PA6-10, average fiber diameter 5.9 μm (coefficient of variation of fiber diameter: 0.20), basis weight 6 g / m² 2 Nonwoven fabric B-6: Polyamide PA6-12, average fiber diameter 6.6 μm (coefficient of variation of fiber diameter: 0.12), basis weight 6 g / m² 2 Nonwoven fabric B-7: Polyamide PA10-10, average fiber diameter 7.7 μm (coefficient of variation of fiber diameter: 0.19), basis weight 6 g / m² 2

[0169] Furthermore, the following nonwoven fabric, manufactured by the spunbond method using the above-mentioned resin raw materials, was used as the resin material layer. Nonwoven fabric B-8: Polyamide PA12, average fiber diameter 49.5 μm (coefficient of variation of fiber diameter: 0.56), basis weight 6 g / m² 2 Nonwoven fabric B-9: Polyamide PA6 / PA12 copolymer, average fiber diameter 42.9 μm (coefficient of variation of fiber diameter: 0.63), basis weight 4 g / m² 2

[0170] Examples 1-4 and Comparative Example 1 Reinforced fiber substrates and fiber-reinforced composite materials (CFRP) according to Examples 1-4 and Comparative Example 1 were manufactured, and the physical properties of the obtained fiber-reinforced composite materials were evaluated. In Examples 1-4 and Comparative Example 1, reinforced fiber substrates having a unidirectional woven fabric were manufactured.

[0171] <Example 1> (Manufacturing of reinforced fiber substrates) The nonwoven fabric B-1 described above was placed on the surface of the unidirectional woven fabric S-1 described above to produce the reinforced fiber base material according to Example 1.

[0172] (Manufacturing of carbon fiber reinforced resin composite materials) Next, a carbon fiber reinforced resin composite material was manufactured using the resin transfer molding (RTM) method with the obtained reinforced fiber substrate and liquid thermosetting resin. First, Release Ply C (AIRTECH), a peel cloth substrate with mold release properties, and Resin Flow 90HT (AIRTECH), a resin diffusion substrate, were laminated onto the substrate. Then, hoses for forming resin injection and discharge ports were placed, the entire structure was covered with a nylon bag film, sealed with sealant tape, and the inside was evacuated. Subsequently, the aluminum plate was heated to 120°C, the pressure inside the bag was reduced to 5 Torr or less, and then the above-mentioned liquid thermosetting resin (matrix resin C-1) heated to 100°C (35 parts by mass per 100 parts by mass of substrate) was injected into the vacuum system through the resin injection port. The injected liquid thermosetting resin filled the bag and impregnated the substrate. The temperature was then raised to 180°C and maintained at 180°C for 2 hours to cure the thermosetting resin, thereby obtaining a carbon fiber reinforced polymer (CFRP) composite material.

[0173] The CAI compressive strength and crack density were measured for the obtained composite material. As shown in Table 1 below, no microcracks occurred in the CFRP manufactured using the reinforced fiber substrate according to Example 1 after the thermal shock test, and the crack density was 0.00 cracks / (cm·ply).

[0174] <Example 2> The reinforced fiber substrate and carbon fiber reinforced resin composite material according to Example 2 were manufactured and evaluated in the same manner as in Example 1, except that nonwoven fabric B-2 was used instead of nonwoven fabric B-1. The evaluation results are shown in Table 1 below.

[0175] <Example 3> The reinforced fiber substrate and carbon fiber reinforced resin composite material according to Example 3 were manufactured and evaluated in the same manner as in Example 1, except that nonwoven fabric B-3 was used instead of nonwoven fabric B-1. The evaluation results are shown in Table 1 below.

[0176] <Example 4> The reinforced fiber substrate and carbon fiber reinforced resin composite material according to Example 4 were manufactured and evaluated in the same manner as in Example 1, except that nonwoven fabric B-4 was used instead of nonwoven fabric B-1. The evaluation results are shown in Table 1 below.

[0177] <Comparative Example 1> The reinforced fiber substrate and carbon fiber reinforced resin composite material according to Comparative Example 1 were manufactured and evaluated in the same manner as in Example 1, except that nonwoven fabric B-8 was used instead of nonwoven fabric B-1. The evaluation results are shown in Table 1 below.

[0178] [Table 1]

[0179] As can be seen in Table 1, in Examples 1 to 4, where the average fiber diameter of the thermoplastic resin fibers constituting the nonwoven fabric was 5.7 to 29.3 μm, the occurrence of microcracks was reduced and the impact resistance of the composite was good compared to Comparative Example 1, where the average fiber diameter was 49.5 μm.

[0180] Examples 5-7 and Comparative Example 2 In Examples 5-7 and Comparative Example 2, a reinforced fiber base material having a non-crimped fabric was prepared, and a thermoplastic resin fiber with a relatively high melting point was used as the thermoplastic resin fiber constituting the nonwoven fabric.

[0181] <Example 5> (Manufacturing of reinforced fiber substrates) Four reinforced fiber sheets were prepared by aligning 200 of the above-mentioned reinforcing fibers (carbon fiber bundles) in one direction. These reinforced fiber sheets were then laminated at angles of -45°, 0°, +45°, and 90°, and the above-mentioned nonwoven fabric B-5 was placed between each layer of reinforced fiber sheets. In this way, a laminated sheet was prepared by laminating four reinforced fiber sheets with fibers aligned in one direction and the nonwoven fabric placed between them.

[0182] Next, stitching thread A-1, used as an auxiliary thread, is used to sew (stitch) the laminated sheet through in the thickness direction, thereby creating the reinforced fiber substrate according to Example 5 (reinforcement fiber basis weight per layer: 190g / m2, stitching thread usage: 4g / m2). 2 Reinforced fiber base material total basis weight: 760g / m 2 ) was obtained.

[0183] (Manufacturing of carbon fiber reinforced resin composite materials) Next, a carbon fiber reinforced resin composite material was manufactured using the resin transfer molding (RTM) method with the obtained reinforced fiber substrate and liquid thermosetting resin. First, Release Ply C (AIRTECH), a peel cloth substrate with mold release properties, and Resin Flow 90HT (AIRTECH), a resin diffusion substrate, were laminated onto the substrate. Then, hoses for forming resin injection and discharge ports were placed, the entire structure was covered with a nylon bag film, sealed with sealant tape, and the inside was evacuated. Subsequently, the aluminum plate was heated to 120°C, the pressure inside the bag was reduced to 5 Torr or less, and then the above-mentioned liquid thermosetting resin (matrix resin C-1) heated to 100°C (35 parts by mass per 100 parts by mass of substrate) was injected into the vacuum system through the resin injection port. The injected liquid thermosetting resin filled the bag and impregnated the substrate. The temperature was then raised to 180°C and maintained at 180°C for 2 hours to cure the thermosetting resin, thereby obtaining a carbon fiber reinforced polymer (CFRP) composite material.

[0184] The CAI compressive strength and crack density were measured for the obtained composite material. The results are shown in Table 2 below.

[0185] <Example 6> The reinforced fiber substrate and carbon fiber reinforced resin composite material according to Example 6 were manufactured and evaluated in the same manner as in Example 5, except that nonwoven fabric B-6 was used instead of nonwoven fabric B-5. The evaluation results are shown in Table 2 below.

[0186] <Example 7> The reinforced fiber substrate and carbon fiber reinforced resin composite material according to Example 7 were manufactured and evaluated in the same manner as in Example 5, except that nonwoven fabric B-7 was used instead of nonwoven fabric B-5. The evaluation results are shown in Table 2 below.

[0187] <Comparative Example 2> The reinforced fiber substrate and carbon fiber reinforced resin composite material according to Comparative Example 2 were manufactured and evaluated in the same manner as in Example 5, except that nonwoven fabric B-9 was used instead of nonwoven fabric B-5. The basis weight of the nonwoven fabric used was 4 g / m². 2 The results were as follows. The evaluation results are shown in Table 2 below.

[0188] [Table 2]

[0189] As can be seen in Table 2, in Examples 5 to 7, where the average fiber diameter of the thermoplastic resin fibers constituting the nonwoven fabric was 5.9 μm to 7.7 μm, the occurrence of microcracks was reduced and the impact resistance of the composite was good compared to Comparative Example 2, where the average fiber diameter was 42.9 μm.

[0190] These results demonstrate that even when the melting point of the thermoplastic resin fibers constituting the nonwoven fabric is relatively high, reducing the fiber diameter of the thermoplastic resin fibers constituting the nonwoven fabric can reduce microcracks and further improve the impact resistance of the composite.

[0191] <<Example 8 and Comparative Examples 3 and 4>> In Example 8 and Comparative Examples 3 and 4, we investigated the case where stitching thread with relatively poor microcrack resistance was used. <Example 8> In Example 8, the reinforced fiber substrate and carbon fiber reinforced resin composite material were manufactured and evaluated in the same manner as in Example 5, except that B-1 was used instead of nonwoven fabric B-5, and A-5 was used instead of stitching thread A-1. The evaluation results are shown in Table 3 below. <Comparative Example 3> In Comparative Example 3, the reinforced fiber substrate and carbon fiber reinforced resin composite material were manufactured and evaluated in the same manner as in Example 8, except that nonwoven fabric B-8 was used instead of nonwoven fabric B-1. The evaluation results are shown in Table 3 below. <Comparative Example 4> In Comparative Example 4, the reinforced fiber substrate and carbon fiber reinforced resin composite material were manufactured and evaluated in the same manner as in Example 8, except that nonwoven fabric B-9 was used instead of nonwoven fabric B-1. The evaluation results are shown in Table 3 below.

[0192] [Table 3]

[0193] The stitching thread A-5 used in Example 8 and Comparative Examples 3 and 4 had a relatively high melting point. When such a stitching thread is used, it is easier for the stitching thread to maintain its shape without melting in the composite, and therefore it is thought that microcracks are relatively likely to occur due to delamination at the interface between the stitching thread and the matrix resin. In fact, as can be seen in Table 3, when stitching thread A-5 was used, the number of microcracks increased compared to when stitching thread with a relatively low melting point was used (Example 1, etc.).

[0194] However, even in such cases, when a small-diameter thermoplastic resin fiber with a single filament diameter of 5.8 μm was used as the resin fiber constituting the nonwoven fabric (Example 8), the occurrence of microcracks was reduced compared to when a thermoplastic resin fiber with a single filament diameter of 49.5 μm or 42.9 μm was used as the resin fiber constituting the nonwoven fabric (Comparative Example 3 or Comparative Example 4). In Comparative Example 4, a nonwoven fabric having thermoplastic resin fibers with a relatively high melting point was used.

[0195] However, the degree of microcrack reduction in Example 8 compared to Comparative Example 3 was smaller than that observed when using a stitching thread with relatively superior performance (for example, the degree of microcrack reduction observed when comparing Example 1 and Comparative Example 1). Although there is no intention to limit this by theory, in the case of stitching threads with relatively poor microcrack resistance, microcracks are more likely to occur due to the stitching thread, so the occurrence of microcracks caused by the nonwoven fabric is relatively reduced, and the effect of selecting the fiber diameter of the thermoplastic resin fibers constituting the nonwoven fabric is relatively less observable.

[0196] Examples 9 to 15 Examples 9-15 further investigated the results when conditions such as the properties of the stitching thread, the application of oil to the stitching thread, and the addition of resin particles were changed.

[0197] <Example 9> In Example 9, a reinforced fiber substrate and a carbon fiber reinforced resin composite material were manufactured and evaluated in the same manner as in Example 8, except that stitching thread A-2 was used instead of stitching thread A-5. The evaluation results are shown in Table 4 below.

[0198] <Example 10> In Example 10, a reinforced fiber substrate and a carbon fiber reinforced resin composite material were manufactured and evaluated in the same manner as in Example 8, except that stitching thread A-3 was used instead of stitching thread A-5. The evaluation results are shown in Table 4 below.

[0199] <Example 11> In Example 11, a reinforcing fiber base material and a carbon fiber reinforced resin composite material were produced and evaluated in the same manner as in Example 8 above, except that A-3 was used instead of stitch yarn A-5 and the stitch yarn was treated with an oil agent. The evaluation results are shown in Table 4 below. In the oil agent treatment, the above oil agent 1 was used.

[0200] <Example 12> In Example 12, a reinforcing fiber base material and a carbon fiber reinforced resin composite material were produced and evaluated in the same manner as in Example 8 above, except that A-4 was used instead of stitch yarn A-5. The evaluation results are shown in Table 4 below.

[0201] <Example 13> In Example 13, a reinforcing fiber base material and a carbon fiber reinforced resin composite material were produced and evaluated in the same manner as in Example 8 above, except that A-1 was used instead of stitch yarn A-5 and resin particles were not added during the production of the composite. In Example 13, matrix resin C-2 was used instead of matrix resin C-1 as the liquid thermosetting resin during the production of the carbon fiber reinforced resin composite material. The evaluation results are shown in Table 4 below.

[0202] <Example 14> In Example 14, a reinforcing fiber base material and a carbon fiber reinforced resin composite material were produced and evaluated in the same manner as in Example 8 above, except that A-6 was used instead of stitch yarn A-5. The evaluation results are shown in Table 4 below.

[0203] <Example 15> In Example 15, a reinforcing fiber base material and a carbon fiber reinforced resin composite material were produced and evaluated in the same manner as in Example 8 above, except that A-7 was used instead of stitch yarn A-5 and three stitch yarns were used together. The evaluation results are shown in Table 4 below.

[0204]

Table 4

[0205] As shown in Table 4, it was confirmed that the occurrence of cracks was well suppressed in Examples 9 to 13. In these examples, the fiber diameter of the thermoplastic resin fibers of the non-woven fabric was relatively thin (5.8 μm), and the micro-crack resistance of the stitch yarn as the auxiliary yarn was relatively good. Therefore, it is considered that the occurrence of cracks was suppressed.

[0206] On the other hand, in the composites according to Examples 14 and 15, the occurrence of micro-cracks was relatively high. The stitch yarn according to Example 14 had a melting point of 257 °C and a relatively high coefficient of linear expansion, so it is considered that its micro-crack resistance was relatively poor. The stitch yarn according to Example 15 had a relatively high total fineness, so it is considered that its micro-crack resistance was relatively poor. However, since Examples 14 and 15 use thermoplastic resin fibers with a relatively thin fiber diameter, it is considered that the occurrence of micro-cracks is suppressed compared to the case of using thermoplastic resin fibers with a relatively thick fiber diameter.

[0207] Also, from Table 4 above, the crack reduction effect by treating the stitch yarn with an oil agent can be seen. That is, in Example 11 using the stitch yarn treated with Oil Agent 1, a better micro-crack density was observed than in Example 10 using the stitch yarn not treated with an oil agent. Note that an epoxy group is introduced into the stitch yarn by Oil Agent 1.

[0208] Furthermore, Table 4 above also shows the effect of suppressing microcracks by using resin particles. That is, the stitching thread A-1 and nonwoven fabric B-1 used in Example 13 both have excellent microcrack resistance, as is clear from Examples 5-7 using stitching thread A-1 and Examples 9-12 using nonwoven fabric B-1. Therefore, when stitching thread A-1 and nonwoven fabric B-1 are used in combination, it is expected that a crack density of about 0.00-0.10 cracks / (cm·ply) will be observed. However, in Example 13, the crack density was relatively high at 0.31 cracks / (cm·ply). Since Example 13 did not contain resin particles, unlike the other examples (especially Examples 5-7 and Examples 9-12, etc.), this result indicates that a microcrack suppression effect can be obtained by including resin particles in the matrix resin constituting the fiber-reinforced composite material. The average particle diameter of the resin particles was 0.11 μm when measured according to the above method for measuring the average particle diameter of resin particles contained in the matrix resin. [Explanation of Symbols]

[0209] 10, 30 Reinforced fiber base material 40 Non-crimped fabric 22, 42 Reinforced Fibers 24, 44 auxiliary threads L direction 110, 310, 312, 314, 316 Resin material layer 130, 330, 340, 350 Reinforced fiber layer

Claims

1. One or more reinforcing fiber layers containing reinforcing fibers, One or more resin material layers containing thermoplastic resin fibers, and auxiliary thread A reinforced fiber substrate having, The auxiliary threads connect the reinforcing fibers to each other and / or the reinforcing fiber layers to each other, thereby maintaining the integrity of the reinforcing fiber layer and / or the reinforcing fiber base material, The average fiber diameter of the thermoplastic resin fibers is 0.5 μm to 35 μm. Reinforced fiber base material.

2. The reinforced fiber substrate according to claim 1, wherein the resin material layer is made of a nonwoven fabric containing thermoplastic resin fibers.

3. The reinforcing fiber substrate according to claim 1 or 2, wherein the thermoplastic resin fiber has a melting point in the range of 130°C to 230°C.

4. The reinforced fiber substrate according to any one of claims 1 to 3, wherein the thermoplastic resin fiber is a fiber of polyamide resin, polyester resin, polyethersulfone (PES) resin, or polyetherimide (PEI) resin.

5. The reinforced fiber base material according to any one of claims 1 to 4, wherein the reinforced fiber layer is a unidirectional fabric having the reinforced fibers aligned in one direction as warp threads and the auxiliary threads as weft threads.

6. The reinforced fiber substrate according to any one of claims 1 to 5, wherein the reinforced fiber substrate includes at least two reinforced fiber layers that are laminated in an overlapping manner, each of the at least two reinforced fiber layers is composed of reinforced fibers aligned in one direction, and the at least two reinforced fiber layers are sewn together by stitching thread as auxiliary thread.

7. The reinforced fiber substrate according to claim 6, wherein the direction of extension of the reinforcing fibers constituting one of the at least two reinforcing fiber layers is different from the direction of extension of the reinforcing fibers constituting the other reinforcing fiber layer.

8. The reinforcing fiber substrate according to any one of claims 1 to 7, wherein each of the one or more resin material layers is disposed on the surface of any of the reinforcing fiber layers.

9. The reinforcing fiber substrate according to any one of claims 1 to 8, wherein at least one of the resin material layers is disposed between the two reinforcing fiber layers.

10. The auxiliary thread used as stitching thread has a fineness of 1 to 75 dtex, and / or Having 1 to 50 filaments, A reinforced fiber base material according to any one of claims 1 to 9.

11. The reinforcing fiber base material according to any one of claims 1 to 10, wherein the auxiliary yarn is made of resin fibers having a melting point of 80 to 185°C.

12. The reinforced fiber substrate according to any one of claims 1 to 11, wherein the auxiliary yarn comprises fibers of polyamide resin, polyester resin, polyethersulfone (PES) resin, or polyetherimide (PEI) resin.

13. The reinforcing fiber substrate according to any one of claims 1 to 12, wherein the auxiliary yarn comprises a compound having at least one selected from the group consisting of a hydroxyl group, an amino group, a phenol group, a lactam group, and an epoxy group, as well as an amide bond and an ester bond.

14. The auxiliary yarn is one that melts when heated at 180°C for 2 hours, or the coefficient of linear expansion in the fiber axis direction of the auxiliary yarn after heating at 180°C for 2 hours and then cooling is -1 × 10 －６ ~80 x 10 －６ A reinforced fiber base material according to any one of claims 1 to 13, wherein the base material is / K.

15. A preform material comprising a reinforcing fiber base material according to any one of claims 1 to 14, and 1 to 20 parts by mass of binder resin per 100 parts by mass of the reinforcing fiber base material.

16. A method for producing a preform, comprising heating a composite comprising a reinforcing fiber base material and a binder resin according to any one of claims 1 to 14 under pressure.

17. A fiber-reinforced resin composite material comprising a reinforced fiber substrate according to any one of claims 1 to 14, and a matrix resin impregnated in the reinforced fiber substrate.

18. A method for producing a fiber-reinforced composite material, comprising impregnating a reinforcing fiber substrate according to any one of claims 1 to 14 with a matrix resin.

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