Reinforced fiber substrate

Abstract

The purpose of the present disclosure is to provide a reinforced fiber substrate that has a resin material layer, exhibits excellent microcrack resistance and sufficient mechanical strength, and exhibits good molding robustness. Th reinforced substrate has one or a plurality of reinforcing fiber layers containing reinforcing fibers, and one or a plurality of resin material layers containing fibers of a thermoplastic resin. The reinforced fiber substrate is characterized in that the melting point of the thermoplastic resin is greater than 180°C and less than or equal to 250°C, and the weight average molecular weight Mw of the thermoplastic resin is 15,000 to 28,000.

Description

Reinforced fiber base material

[0001] The present invention relates to a reinforcing fiber substrate and a method for producing the same. The present invention also relates to a preform material and a fiber-reinforced composite material having the reinforcing fiber substrate, and methods for producing them.

[0002] Fiber-reinforced composite materials (also referred to as fiber-reinforced resin composite materials or composites) are lightweight, high-strength, and highly rigid, and are therefore used in a wide range of fields, including sports and leisure applications such as fishing rods and golf shafts, and industrial applications such as automobiles and aircraft. Fiber-reinforced composite materials can be produced, for example, by impregnating a reinforcing fiber substrate (particularly a reinforcing fiber substrate made of carbon fiber) with a matrix resin and then curing the matrix resin. Methods for molding fiber-reinforced composite materials include a method in which a reinforcing fiber substrate is pre-impregnated with a resin and then molded into a sheet-like prepreg (intermediate substrate), as well as a method (resin transfer molding, RTM) in which a reinforcing fiber substrate placed in a mold is impregnated with a liquid resin (i.e., an uncured curable resin or a molten thermoplastic resin) and then cured or solidified to obtain a fiber-reinforced composite material.

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

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

[0005] Furthermore, a non-crimp fabric can also be used as the reinforcing fiber substrate. In a non-crimp fabric, a plurality of reinforcing fiber layers made of reinforcing fibers aligned in one direction are laminated, and these laminated reinforcing fiber layers are sewn together with a stitch thread as an auxiliary thread. In a non-crimp fabric, a laminate of reinforcing fiber sheets made of reinforcing fibers aligned in one direction is integrated by being sewn together with an auxiliary thread (particularly called a stitch thread) that penetrates the laminate in the thickness direction.

[0006] It is known to use a resin material layer (also called a veil layer) such as a nonwoven fabric in such a reinforcing fiber substrate. The resin material layer is generally composed of thermoplastic resin fibers. For example, a nonwoven fabric containing thermoplastic resin fibers as the resin material layer can be disposed on and / or between the reinforcing fiber layers. This resin material layer can provide advantageous effects in terms of interlaminar fracture toughness, impact resistance, resin permeability, and dimensional stability of the substrate.

[0007] US Patent No. 5,949,999 describes a reinforcing element for a curable composition comprising a resin-soluble thermoplastic veil suitable for being positioned between reinforcing fiber layers.

[0008] US Patent No. 5,949,999 describes an intermediate material intended to be combined with a thermosetting resin to produce a composite part, the intermediate material consisting of a unidirectional layer of carbon fibers combined on each side with a web of thermoplastic fibers having a specific thickness.

[0009] Patent Document 3 describes a reinforcing fiber substrate, which has a reinforcing fiber assembly and a mesh-like resin material arranged on at least one surface thereof, and the resin material is a copolymer polyamide containing at least two polyamide components selected from polyamide 6, polyamide 6-6, polyamide 6-10, polyamide 12, and polyamide 6-I, and the melting point of the resin material is within the range of 80 to 180°C.

[0010] JP 2008-540766 A JP 2012-506499 A JP 2019-99987 A

[0011] Fiber-reinforced composite materials manufactured from reinforcing fiber substrates are required to have excellent microcrack resistance, sufficient mechanical strength, and good molding robustness. However, conventional reinforcing fiber substrates having a resin material layer (veil layer) have difficulty in satisfying all of these properties.

[0012] An object of the present invention is to provide a reinforcing fiber substrate having a resin material layer, which exhibits excellent microcrack resistance, sufficient mechanical strength, and good molding robustness. Another object of the present invention is to provide a preform material and a fiber-reinforced composite material having such a reinforcing fiber substrate, and to provide methods for producing them.

[0013] Microcracks are minute cracks measuring several to several tens of micrometers that can occur in fiber-reinforced composite materials, particularly those used in aerospace applications. These microcracks are likely to occur in environments where hundreds of thermal shock cycles accompanied by rapid temperature changes from high temperatures of approximately 70 to 100°C to low temperatures of approximately -50 to -60°C are repeated. The matrix resin contained in the fiber-reinforced composite material tends to shrink as the temperature drops from high to low, but the reinforcing fibers, which have a relatively low coefficient of linear thermal expansion relative to the matrix resin, suppress deformation of the matrix resin, resulting in the accumulation of residual thermal stress within the matrix resin. Microcracks are likely to occur due to the accumulation of fatigue stress caused by such thermal shock cycles. Similarly, auxiliary yarns and nonwoven fibers contained in reinforcing fiber substrates often have a different coefficient of linear thermal expansion from the matrix resin. Residual thermal stress concentrates at the interface of fiber-reinforced composite materials containing these materials, easily causing interfacial delamination and microcracks originating from the interface.

[0014] The problems associated with the present disclosure can be solved by the following aspects of the present invention. <Aspect 1> A reinforcing fiber substrate having one or more reinforcing fiber layers containing reinforcing fibers, and one or more resin material layers containing fibers of a thermoplastic resin, wherein the melting point of the thermoplastic resin is greater than 180°C and not greater than 250°C, and the weight-average molecular weight Mw of the thermoplastic resin is 15,000 to 28,000. <Aspect 2> The reinforcing fiber substrate according to Aspect 1, wherein the polydispersity (Mw / Mn) of the thermoplastic resin is 1.40 to 1.80. <Aspect 3> The reinforcing fiber substrate according to Aspect 1 or 2, wherein the thermoplastic resin is a polyamide resin or a polyester resin. <Aspect 4> The reinforcing fiber substrate according to any one of Aspects 1 to 3, wherein the thermoplastic resin is a polyamide resin. <Aspect 5> The reinforcing fiber substrate according to any one of Aspects 1 to 4, wherein the average fiber diameter of the fibers of the thermoplastic resin is 1 μm to 60 μm. <Aspect 6> The reinforcing fiber substrate according to any one of Aspects 1 to 5, wherein the one or more resin material layers are made of a nonwoven fabric containing thermoplastic resin fibers. <Aspect 7> The reinforcing fiber substrate according to Aspect 6, wherein the one or more resin material layers are made of a long-fiber nonwoven fabric containing thermoplastic resin fibers. <Aspect 8> The reinforcing fiber substrate according to any one of Aspects 1 to 7, wherein the one resin material layer or each of the plurality of resin material layers is disposed on a surface of the one reinforcing fiber layer or on a surface of any of the plurality of reinforcing fiber layers. <Aspect 9> The reinforcing fiber substrate according to any one of Aspects 1 to 8, wherein the reinforcing fiber layer is a unidirectional woven fabric having the reinforcing fibers aligned in one direction as warp yarns and auxiliary yarns as weft yarns. <Aspect 10> The reinforcing fiber substrate according to any one of Aspects 1 to 8, wherein the reinforcing fiber substrate includes at least two reinforcing fiber layers stacked on top of each other, each of the at least two reinforcing fiber layers being composed of the reinforcing fibers aligned in one direction, and the at least two reinforcing fiber layers being sewn together with a stitch yarn as an auxiliary yarn. <Aspect 11> The reinforcing fiber substrate according to any one of Aspects 1 to 10, wherein the reinforcing fibers are carbon fibers. <Aspect 12> A preform material comprising the reinforcing fiber substrate according to any one of Aspects 1 to 11 and a binder resin.<Aspect 13> A method for producing a preform material, comprising heating under pressure a composite comprising the reinforcing fiber substrate according to any one of Aspects 1 to 11 and a binder resin. <Aspect 14> A fiber-reinforced resin composite material having the reinforcing fiber substrate according to any one of Aspects 1 to 11, and a matrix resin impregnated into the reinforcing fiber substrate. <Aspect 15> A method for producing a fiber-reinforced composite material, comprising: impregnating the reinforcing fiber substrate according to any one of Aspects 1 to 11 with a matrix resin; and subjecting the reinforcing fiber substrate impregnated with the matrix resin to a heat-curing treatment to obtain a fiber-reinforced composite material.

[0015] According to the present invention, it is possible to provide a reinforcing fiber substrate having a resin material layer, which exhibits excellent microcrack resistance, sufficient mechanical strength, and good molding robustness.

[0016] Furthermore, according to the present invention, it is possible to provide a preform material and a fiber-reinforced composite material having such a reinforcing fiber substrate, and further to provide methods for producing these.

[0017] Figure 1 shows a cross-sectional schematic view of a reinforcing fiber substrate according to one embodiment of the present invention. Figure 2 shows a perspective schematic view of the reinforcing fiber layer of Figure 1. Figure 3 shows a cross-sectional schematic view of a reinforcing fiber substrate according to another embodiment of the present invention. Figure 4 shows a perspective view of a plurality of reinforcing fiber layers of Figure 3.

[0018] <<Reinforcing Fiber Substrate>> The reinforcing fiber substrate according to the present disclosure has one or more reinforcing fiber layers containing reinforcing fibers, and one or more resin material layers containing thermoplastic resin fibers, wherein the thermoplastic resin has a melting point greater than 180°C and not greater than 250°C, and the thermoplastic resin has a weight average molecular weight Mw of 15,000 to 28,000.

[0019] In the past, when high-melting-point thermoplastic resin fibers were used in the resin material layer (veil layer), it was thought that their low affinity with the matrix resin resulted in poor mechanical properties and microcrack resistance. Therefore, a method of overcoming this disadvantage by using thermoplastic resin fibers with a relatively low melting point for the veil layer has been proposed.

[0020] The present inventors have found that when thermoplastic resin fibers with a relatively low melting point are used, the resin material layer melts during the heat treatment when molding the fiber-reinforced composite material, which can adversely affect the molding robustness of the fiber-reinforced composite material. That is, the thickness can change depending on the curing rate.

[0021] In contrast, in the present invention, a high-melting point thermoplastic resin fiber is used as the resin material layer, and the molecular weight of the thermoplastic resin is optimized, thereby making it possible to obtain a reinforcing fiber substrate that is excellent in mechanical strength and microcrack resistance as well as molding robustness.

[0022] In particular, according to the present invention, the resin material layer contains high-melting-point resin fibers, thereby ensuring good molding robustness, and the molecular weight of the resin of the thermoplastic resin fibers that make up the resin material layer is limited to a relatively low range, thereby improving the affinity (adhesion) with the matrix resin in the composite material, thereby ensuring good microcrack resistance.

[0023] Although not intending to be limited by theory, when the molecular weight of the thermoplastic resin is relatively low, the molecular chains of the thermoplastic resin forming the resin material layer are more likely to become loosely entangled during heat treatment than when the molecular weight is high. Therefore, it is thought that the matrix resin is more likely to enter the gaps between the molecular chains of the thermoplastic resin forming the resin material layer that have been loosened by heating, and the molecular chains of the thermoplastic resin forming the resin material layer and the matrix resin are more likely to become entangled. As a result, it is thought that the interfacial adhesive strength (affinity) between the resin material layer and the matrix resin in the composite material is improved.

[0024] Furthermore, the reinforcing fiber substrate according to the present invention exhibits sufficient mechanical properties (particularly compressive properties after impact) of a fiber reinforced composite material formed from this reinforcing fiber substrate.

[0025] The components of the present invention will be described in detail below.

[0026] <Reinforcing fiber substrate> The reinforcing fiber substrate according to the present invention has one or more reinforcing fiber layers and one or more resin material layers. The presence of a resin material layer in the reinforcing fiber substrate can have advantageous effects, particularly on the interlaminar fracture toughness and impact resistance of the fiber-reinforced composite material. The reinforcing fiber substrate according to the present invention can be produced, for example, by a method including arranging a resin material layer on the surface of a reinforcing fiber layer, based on the description of the present disclosure and known techniques.

[0027] The reinforcing fiber substrate according to the present disclosure preferably has a fiber density of 100 to 2000 g / m ２ , more preferably 150 to 1500 g / m ２ The thickness of the reinforcing fiber substrate according to the present disclosure can be appropriately selected depending on the application of the molded product, and may be 0.1 to 2 mm, or 0.5 to 1.5 mm.

[0028] To facilitate understanding of the present invention, exemplary structures of reinforcing fiber substrates according to the present disclosure will be described in outline with reference to the drawings, which are schematic views for facilitating understanding of the present invention, are not to scale, and are not intended to limit the present invention.

[0029] FIG. 1 shows a cross-sectional schematic diagram of the minimum configuration of a reinforcing fiber substrate 10 according to one embodiment of the present invention. The reinforcing fiber substrate 10 includes a resin material layer 110 and a reinforcing fiber layer 130 that are stacked on top of each other. The resin material layer 110 is disposed on the surface of the reinforcing fiber layer 130. The resin material layer 110 includes thermoplastic resin fibers (fibers of a thermoplastic resin). The resin material layer 110 may be a nonwoven fabric made of thermoplastic resin fibers. The reinforcing fiber layer 130 is made of reinforcing fibers aligned in one direction. Although not shown, the reinforcing fibers and / or the reinforcing fiber layers may be connected to each other by auxiliary yarns, thereby maintaining the integrity of the reinforcing fiber layers and / or the reinforcing fiber substrate.

[0030] FIG. 2 shows a schematic perspective view of the reinforcing fiber layer 130 of FIG. 1. The resin material layer 110 is not shown in FIG. 2. In the embodiment of FIG. 2, the reinforcing fiber layer 130 is a unidirectional woven fabric (UD-woven fabric). A unidirectional woven fabric is a so-called "tread fabric" and is composed of reinforcing fibers (particularly bundles of reinforcing fibers) 22 aligned in one direction and auxiliary yarns 24. The reinforcing fibers 22 as warp yarns and the auxiliary yarns 24 as weft yarns intertwine to form the woven fabric.

[0031] 1 and 2, the minimum configuration of the reinforcing fiber substrate having one reinforcing fiber layer and one resin material layer is described, but the reinforcing fiber substrate may have a plurality of reinforcing fiber layers and / or resin material layers. For example, a resin material layer may be laminated between a plurality of reinforcing fiber layers.

[0032] 3 shows a cross-sectional schematic view of a reinforcing fiber substrate 30 according to another embodiment of the present invention. The reinforcing fiber substrate 30 includes a plurality of laminated resin material layers 310-316 and a plurality of reinforcing fiber layers 330, 340, and 350. The resin material layers 312 and 314 are disposed between the reinforcing fiber layers 330, 340, and 350, respectively. The resin material layers 310 and 316 are disposed as the outermost layers. The resin material layers 310-316 may be nonwoven fabrics made of thermoplastic resin fibers. The reinforcing fiber layers 330, 340, and 350 are made of reinforcing fibers aligned in one direction. Although not shown, the reinforcing fibers of the reinforcing fiber layers 330, 340, and 350 may be connected to each other by auxiliary threads, and / or the reinforcing fiber layers 330, 340, and 350 may be connected to each other by auxiliary threads, thereby maintaining the shape (particularly the sheet shape) of the reinforcing fiber layers 330, 340, and 350 and the integrity of the reinforcing fiber substrate 30.

[0033] FIG. 4 is a perspective view corresponding to the reinforcing fiber substrate of FIG. 3 . In FIG. 4 , the resin material layers 310-316 are not shown. The multiple reinforcing fiber layers 330, 340, and 350 in FIG. 4 constitute a non-crimp fabric 40. That is, the reinforcing fiber layers 330, 340, and 350 are each formed from reinforcing fibers 42 aligned in one direction, and these stacked reinforcing fiber layers are integrated by stitching with a stitch thread 44 as an auxiliary thread. The stitch thread 44 as an auxiliary thread 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 FIG. 4 . In a non-crimp fabric, bending of the reinforcing fibers is less likely to occur, which can further improve the mechanical properties of a fiber-reinforced composite material manufactured from the reinforcing fiber substrate.

[0034] In the embodiment shown in Fig. 4, the reinforcing fibers constituting each of the multiple reinforcing fiber layers extend in different directions. That is, the reinforcing fibers constituting reinforcing fiber layer 330 extend along direction L shown in Fig. 4, the reinforcing fibers constituting reinforcing fiber 340 extend at an angle of approximately 90° to direction L, and the reinforcing fibers constituting reinforcing fiber 450 extend at an angle of approximately 45° to direction L.

[0035] The resin material layers 310 to 316 arranged on the reinforcing fiber layers can also be sewn together with the multiple reinforcing fiber layers by auxiliary threads 44 .

[0036] <Reinforcing Fiber Layer> The reinforcing fiber layer contains reinforcing fibers.

[0037] As the reinforcing fiber layer, for example, a reinforcing fiber sheet can be used, and in particular, a reinforcing fiber sheet obtained by processing continuous fiber bundles of reinforcing fibers into a sheet shape can be used. In one embodiment according to the present disclosure, the reinforcing fiber layer is unidirectional (UD: Uni-directional). That is, the reinforcing fiber layer is formed from reinforcing fibers aligned in one direction.

[0038] In one embodiment according to the present disclosure, the reinforcing fiber layer is a unidirectional woven fabric (UD-woven fabric) having reinforcing fibers aligned in one direction as warp yarns and auxiliary yarns as weft yarns (see FIG. 2 above).

[0039] In another embodiment according to the present disclosure, the reinforcing fiber substrate is a non-crimp fabric (NCF) (see FIG. 4 described above). As described above, the non-crimp fabric includes at least two reinforcing fiber layers stacked on top of each other, each of which is made of reinforcing fibers aligned in one direction, and which are sewn together with a stitch yarn serving as an auxiliary yarn.

[0040] Preferably, in the reinforcing fiber substrate according to the present disclosure, the extending direction of the reinforcing fibers in one of the at least two reinforcing fiber layers is different from the extending direction of the reinforcing fibers in the other reinforcing fiber layer. In particular, a plurality of reinforcing fiber layers made of reinforcing fibers aligned in one direction are sequentially stacked with their fiber axis directions changed from one another. This embodiment is preferable because it improves the isotropy of the reinforcing fiber substrate.

[0041] (Reinforcing Fiber) Examples of reinforcing fiber include carbon fiber, glass fiber, aramid fiber, boron fiber, metal fiber, etc. The reinforcing fiber is preferably carbon fiber.

[0042] The average length of the reinforcing fibers is not particularly limited, but may be, for example, 5 cm to 100 m.

[0043] (Auxiliary Yarn) The reinforcing fiber layer according to the present disclosure may have auxiliary yarns. As described above with reference to Figures 2 and 4, the auxiliary yarns can serve to maintain the integrity of the reinforcing fiber layer and / or the reinforcing fiber substrate by connecting the reinforcing fibers and / or the reinforcing fiber layers to each other.

[0044] In one embodiment, the auxiliary yarns serve as wefts to the reinforcing fibers serving as warps. For example, the auxiliary yarns as wefts cross the reinforcing fibers aligned in one direction at an angle of approximately 90° to form a unidirectional fabric (see FIG. 2 above).

[0045] In another embodiment, the auxiliary thread is a stitch thread. The method of stitching the reinforcing fiber substrate with the stitch thread is not particularly limited, but the stitch thread sews together, for example, a plurality of reinforcing fiber layers made of reinforcing fibers aligned in one direction in a laminate in which the reinforcing fiber layers are stacked (see FIG. 4 above).

[0046] The auxiliary yarn preferably has a fineness of 1 dtex to 75 dtex, more preferably 15 dtex to 40 dtex.

[0047] In one preferred embodiment of the present invention, the auxiliary yarns comprise fibers of polyolefin fibers, polyamide resins, polyester resins, cellulose fibers, polyethersulfone (PES) resins, or polyetherimide (PEI) resins, or mixtures thereof, or may consist of at least one of these.

[0048] <Resin Material Layer> The resin material layer contains fibers of a thermoplastic resin (thermoplastic resin fibers).

[0049] The resin material layer can be laminated together with the reinforcing fiber layer to form a laminate, as illustrated in Figs. 1 and 3, for example. The resin material layer may be disposed between the reinforcing fiber layers in such a laminate. Preferably, the resin material layer is adjacent to the reinforcing fiber layer, and in particular, disposed on the surface of the reinforcing fiber layer. By having the resin material layer in the reinforcing fiber substrate, the impact resistance of the fiber-reinforced resin composite material manufactured from the reinforcing fiber substrate can be improved. The reinforcing fiber layer and the resin material layer may be bonded to each other by a binder. For details about the binder, see the description of the preform material below.

[0050] When the reinforcing fiber layer is a unidirectional woven fabric, the resin material layer may be disposed, for example, on a main surface of the unidirectional woven fabric.

[0051] When the reinforcing fiber substrate has a non-crimp fabric, the resin material layer may be arranged as the outermost layer (i.e., for example, on one or both main surfaces of a laminate consisting of multiple reinforcing fiber layers), and / or may be arranged between multiple reinforcing fiber layers that make up the non-crimp fabric.

[0052] The resin material layer (particularly the 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.

[0053] The weight of the resin material layer is preferably 1 g / m ２ ~15g / m ２ , more preferably 2 g / m ２ ~10g / m ２ , particularly preferably 4 g / m ２ ~6g / m ２ is.

[0054] In one embodiment of the reinforcing fiber substrate according to the present disclosure, a resin material layer is disposed on a surface of a reinforcing fiber layer. More specifically, one resin material layer or each of a plurality of resin material layers is disposed on a surface of one reinforcing fiber layer or on the surface of any of the plurality of reinforcing fiber layers.

[0055] In one preferred embodiment according to the present disclosure, the resin material layer is a sheet containing thermoplastic resin fibers, particularly a nonwoven fabric containing thermoplastic resin fibers.

[0056] In one embodiment of the present disclosure, the resin material layer is a nonwoven fabric containing thermoplastic resin fibers, more preferably a nonwoven fabric made of thermoplastic resin fibers. The nonwoven fabric can be produced by a meltblowing method or a spunbonding method. The meltblowing method allows for the production of a thinner nonwoven fabric containing thermoplastic resin fibers with a smaller fiber diameter than the spunbonding method. On the other hand, the spunbonding method produces a nonwoven fabric with a larger fiber diameter than the fibers produced by the meltblowing method, resulting in superior strength and ease of handling.

[0057] In one embodiment according to the present disclosure, the resin material layer is made of a long-fiber nonwoven fabric containing thermoplastic resin fibers, where the long-fiber nonwoven fabric refers to a fabric made of continuous thermoplastic resin fibers having a length of 1 m or more.

[0058] (Thermoplastic Resin Fibers) The resin material layer contains thermoplastic resin fibers (also referred to as thermoplastic resin fibers).

[0059] The mass ratio of the thermoplastic resin fiber to the resin material layer is preferably 50 mass % or more, more preferably 80 mass % or more, and particularly preferably 90 mass % or more. In particular, the resin material layer is made of thermoplastic resin fiber.

[0060] (Melting point of thermoplastic resin) The thermoplastic resin constituting the thermoplastic resin fiber according to the present disclosure has a melting point of more than 180° C. and not more than 250° C. As described above, this makes it possible to provide a reinforcing fiber substrate having good molding robustness.

[0061] The melting point of the thermoplastic resin may be 181° C. or higher, 182° C. or higher, or 183° C. or higher, and / or 245° C. or lower, 240° C. or lower, 235° C. or lower, 230° C. or lower, 225° C. or lower, or 220° C. or lower. The melting point of the thermoplastic resin is preferably 180° C. to 240° C., more preferably 181° C. to 230° C., and even more preferably 182° C. to 220° C.

[0062] The melting point of the thermoplastic resin fiber can be measured using a differential scanning calorimeter in accordance with JIS K7121 under the following conditions: Measurement temperature range: room temperature to 250°C Heating rate: 5°C / min

[0063] (Weight-average molecular weight of thermoplastic resin) The thermoplastic resin constituting the thermoplastic resin fiber according to the present invention has a weight-average molecular weight (Mw) of 15,000 to 28,000. As described above, by limiting the molecular weight of the resin of the thermoplastic resin fiber to a relatively low range, the affinity (adhesion) with the matrix resin in the composite material is improved, thereby achieving good microcrack resistance.

[0064] The weight average molecular weight (Mw) of the thermoplastic resin may be 16,000 or more, 17,000 or more, or 18,000 or more, and / or 27,500 or less, 27,000 or less, 26,500 or less, 26,000 or less, 25,500 or less, 25,000 or less, or 24,500 or less. The weight average molecular weight (Mw) of the thermoplastic resin is preferably 16,000 to 27,000, more preferably 16,500 to 26,000, and even more preferably 17,000 to 25,000.

[0065] The weight average molecular weight (Mw) of the thermoplastic resin can be determined by Gel Permeation Chromatography (GPC).

[0066] (Number Average Molecular Weight of Thermoplastic Resin) The thermoplastic resin constituting the thermoplastic resin fiber according to the present disclosure preferably has a number average molecular weight (Mn) of 10,000 to 15,000. This number average molecular weight (Mn) of the thermoplastic resin is more preferably 10,500 to 15,000, and particularly preferably 11,000 to 14,500.

[0067] (Polydispersity of Thermoplastic Resin) The polydispersity (Mw / Mn) of the thermoplastic resin constituting the thermoplastic resin fiber according to the present disclosure may be 1.00 to 2.50. This polydispersity is preferably 1.30 to 2.00, more preferably 1.40 to 1.80, and even more preferably 1.45 to 1.75. By limiting the polydispersity of the resin of the thermoplastic resin fiber to a relatively low range, the variation in molecular weight of the thermoplastic resin is reduced, and the probability of the presence of high-molecular-weight regions in the thermoplastic resin fiber can be reduced. Therefore, when the polydispersity of the thermoplastic resin is limited to a relatively low range, the probability of the presence of regions with low affinity (adhesion) between the thermoplastic resin material and the matrix resin can be reduced.

[0068] The polydispersity (Mw / Mn) of the thermoplastic resin can be calculated from the weight average molecular weight and number average molecular weight of the thermoplastic resin determined by GPC.

[0069] (Glass transition temperature / softening temperature of thermoplastic resin) The present disclosure also includes an embodiment in which the resin material layer contains fibers of a thermoplastic resin that does not have a melting point, or is even composed of a thermoplastic resin that does not have a melting point.

[0070] When the resin material layer contains fibers of a thermoplastic resin that does not have a melting point (or is composed of such fibers), the thermoplastic resin that does not have a melting point has a glass transition temperature of 180 to 230° C. That is, in one aspect included in the present disclosure, the thermoplastic resin of the thermoplastic resin fibers of the resin material layer has a melting point of more than 180° C. and not more than 250° C. and / or the thermoplastic resin has a glass transition temperature of 180 to 230° C.

[0071] The glass transition temperature of a thermoplastic resin can be measured using a differential scanning calorimeter in accordance with JIS K7121 under the following conditions: Measurement temperature range: -50 to 300°C Temperature rise rate: 10°C / min

[0072] (Types of Thermoplastic Resins) Thermoplastic resins constituting the thermoplastic resin fibers include polyamide, polyimide, polyamide-imide, polyester, polybutadiene, polyurethane, polypropylene, polyetherimide (PEI), polysulfone, polyethersulfone (PES), polyphenylsulfone, polyphenylene sulfide (PPS), polyetherketone, polyetheretherketone (PEEK), polyarylamide, polyketone, polyphthalamide (PPA), polyphenylene ether, polybutylene terephthalate, polyethylene terephthalate, polyester-polyarylate, aramid, polybenzoxazole, and viscose. The thermoplastic resin fibers can include at least one of these thermoplastic resins, and are particularly formed from at least one of these thermoplastic resins.

[0073] In a preferred embodiment of the present invention, the thermoplastic resin constituting the thermoplastic resin fiber includes a polyamide resin or a polyester resin, and particularly preferably includes a polyamide resin (PA resin), and is particularly preferably a polyamide resin or a polyester resin, and particularly preferably a polyamide resin (PA resin).

[0074] (Polyamide Resin) Examples of polyamide resins include PA6, PA12, PA11, PA66, PA610, PA612, PA1010, and PA6 / PA12 copolymers.

[0075] Among the polyamide resins, PA11 and PA612 are more preferred, and PA11 is most preferred. When these polyamide resins are used, it is easy to obtain thermoplastic resin fibers that satisfy the melting point and molecular weight according to the present invention.

[0076] (Average fiber diameter) In a preferred embodiment according to the present disclosure, the average fiber diameter of the thermoplastic resin fiber is 1 μm to 60 μm. When the average fiber diameter of the thermoplastic resin fiber is within this range, a reinforcing fiber substrate having further improved resistance to microcracks can be obtained.

[0077] The average fiber diameter is preferably 2 μm to 58 μm, more preferably 3 μm to 55 μm, particularly preferably 4 μm to 45 μm or even 5 μm to 42 μm. In one particularly preferred embodiment, the average fiber diameter is 1 μm to 12 μm, 3 μm to 10 μm, or even 4 μm to 8 μm.

[0078] The average fiber diameter of the thermoplastic fibers can be determined by averaging the fiber diameter values ​​measured for at least 30 fibers using an optical microscope.

[0079] <Preform Material> The present disclosure also includes a preform material having a reinforcing fiber substrate according to the present invention. When a fiber-reinforced composite material is molded using the reinforcing fiber substrate of the present invention, the reinforcing fiber substrate can be used as is, but from the viewpoint of handleability and workability, it is preferable to use a preform material preformed by stacking reinforcing fiber substrates.

[0080] The preform material according to the present disclosure may include the reinforcing fiber substrate according to the present invention and a binder resin.

[0081] (Binder Resin) The resin material used as the binder resin is not particularly limited, and 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 powder, or may be formed into sheets, nonwoven fabrics, etc. and laminated on the reinforcing fiber substrate of the present invention. Alternatively, they may be attached in advance to each yarn constituting the reinforcing fiber substrate of the present invention.

[0082] The amount of binder resin constituting the preform material is preferably 1 to 20 parts by mass, more preferably 5 to 10 parts by mass, per 100 parts by mass of the reinforcing fiber substrate of the present invention. In one embodiment according to the present disclosure, the preform material comprises the reinforcing fiber substrate according to the present disclosure and 1 to 20 parts by mass of the binder resin per 100 parts by mass of the reinforcing fiber substrate.

[0083] The thickness of the preform material varies depending on the purpose of use, but is preferably 1 to 40 mm.

[0084] <Production of Preform Material> The method for producing the preform material according to the present disclosure is not particularly limited, but it can be preferably produced by a method including heating under pressure a composite (precursor composite) containing a reinforcing fiber substrate and a binder resin (particularly a composite (precursor composite) composed of these).

[0085] Specifically, for example, the preform material is produced by stacking the reinforcing fiber substrate of the present invention, or the reinforcing fiber substrate of the present invention and another reinforcing fiber substrate, on one side of a preform production mold to the desired thickness, and if necessary, scattering powder of a binder resin (binder resin) or laminating a resin sheet, and preforming by heating under pressure using a press or the like using a heating plate. The resin melts upon heating, and the reinforcing fiber substrates of the present invention, or the reinforcing fiber substrate of the present invention and another reinforcing fiber sheet, are molded according to the mold, resulting in a preform material that retains the shape of the mold. The conditions for heating under pressure can be set appropriately depending on the type of constituent elements of the preform material (e.g., binder resin).

[0086] The preform material can be made into a fiber-reinforced composite material by a known molding method such as the RTM method or the RFI method. The preform material produced by the above method retains its three-dimensional shape even after preforming. Therefore, the preform material can be transferred from the preform production mold to the fiber-reinforced composite material production mold without losing its shape. Therefore, there is no need to directly stack the preform material on the mold used to produce the fiber-reinforced composite material, which reduces the time the mold is occupied and improves the productivity of the fiber-reinforced composite material.

[0087] <Fiber-reinforced composite material> The present disclosure also includes a fiber-reinforced composite material (fiber-reinforced plastic, FRP; also called a composite) having the reinforcing fiber substrate according to the present disclosure. This fiber-reinforced composite material has the reinforcing fiber substrate according to the present disclosure and a matrix resin impregnated into the reinforcing fiber substrate.

[0088] (Matrix Resin) A thermosetting resin or a thermoplastic resin is used as the matrix resin. When the matrix resin contains a thermosetting resin, the content of the thermosetting resin may be 30% by mass or more, 40% by mass or more, or 50% by mass or more, and / or 100% by mass or less, 90% by mass or less, 80% by mass or less, or 70% by mass or less, based on the mass of the matrix resin.

[0089] 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 resins and cyanate ester resins, urethane acrylate resins, phenoxy resins, alkyd resins, urethane resins, bismaleimide resins, polyimide resins and polyisoimide resins having acetylene terminals, and polyimide resins having Nadic acid terminals. These resins can be used alone or as a mixture 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.

[0090] (Epoxy Resin) The epoxy resin that can be used for the thermosetting resin that can be used in the present invention is not particularly limited, and examples thereof 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; and trifunctional epoxy resins such as triglycidyl-m-aminophenol, triglycidyl-p-aminophenol, and triglycidyl isocyanurate. Examples of the epoxy resin include diglycidyl aniline and its derivatives such as diglycidyl-o-toluidine, diglycidyl-m-toluidine, diglycidyl-p-toluidine, diglycidyl-xylidine, diglycidyl-mesidine, diglycidyl-anisidine, diglycidyl-phenoxyaniline, diglycidyl-naphthylamine and its derivatives, and bifunctional epoxy resins such as bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, bisphenol S diglycidyl ether, resorcinol diglycidyl ether, and 1,6-naphthalenediol diglycidyl ether. These epoxy resins may be used alone or in combination.

[0091] (Curing Agent) A known curing agent can be used for the thermosetting resin that can be used in the present invention. In particular, it is preferable to use an amine-based curing agent from the viewpoint of the mechanical properties of the cured product. The thermosetting resin that can be used in the present invention may or may not contain this curing agent in advance. A thermosetting resin that does not contain a curing agent is in a state that can be mixed with the curing agent before or during curing.

[0092] Examples of the amine-based curing agent include latent curing agents such as dicyandiamide, aliphatic polyamines, various isomers of aromatic polyamine-based curing agents, aminobenzoic acid esters, and acid anhydrides. Dicyandiamide is preferred because it provides excellent storage stability to the reinforcing fiber substrate impregnated with the matrix resin.

[0093] The curing agent suitable for the RTM molding method may be any polyamine having the above structure, and specific examples include 4,4'-diaminodiphenylmethane and its derivatives, and phenylenediamine and its derivatives.

[0094] 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 of the thermosetting resins (particularly all of the epoxy compounds) blended in the matrix resin, and is adjusted appropriately depending on the types of thermosetting resins (particularly the epoxy compounds) and curing agents used.

[0095] Specifically, for example, the ratio of the number of epoxy groups contained in the epoxy compound in the matrix resin to the number of active hydrogen atoms contained 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 exceeds 1.3, the molar balance between epoxy groups and active hydrogen atoms will be disrupted, and the crosslink density of the resulting cured resin may be insufficient, and mechanical properties such as heat resistance, elastic modulus, and fracture toughness may be reduced.

[0096] When the matrix resin contains a thermosetting resin, the matrix resin may contain, in addition to a curing agent and a curing accelerator, a colorant, a filler, various additives, etc. To improve the impact resistance of the matrix resin, it is preferable to contain a thermoplastic resin component or resin particles. Examples of resin particles that can be used include thermoplastic resin particles, thermosetting resin particles, and rubber particles, with rubber particles being preferred. Examples of rubber particles include silicone rubber, polybutadiene rubber, and styrene butadiene rubber. Resin particles may be used alone or in combination of two or more types. The average particle diameter of the resin particles may be 0.01 μm to 1.0 μm, or even 0.03 μm to 0.3 μm. The average particle diameter of the resin particles can be determined by observing the cross section of a fiber-reinforced composite material with a scanning electron microscope or a transmission electron microscope, measuring the diameters of at least 50 resin particles, and averaging them. Observation can be performed at 25,000x magnification. When the resin particles are not perfectly round, that is, when the resin particles are elliptical or the like, the maximum diameter of the resin particles can be used as the particle diameter of the resin particles.

[0097] (Thermoplastic Resin Component) The matrix resin may further contain a thermoplastic resin in addition to the thermosetting resin. Examples of the thermoplastic resin include an epoxy resin-soluble thermoplastic resin and an epoxy resin-insoluble thermoplastic resin.

[0098] The epoxy resin-soluble thermoplastic resin adjusts the viscosity of the matrix resin and improves the impact resistance of the resulting fiber-reinforced composite material. This epoxy resin-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.

[0099] Here, "partially dissolved in epoxy resin" means that when 100 parts by mass of epoxy resin is mixed with 10 parts by mass of thermoplastic resin having an average particle size of 20 to 50 μm and the mixture is stirred at 190°C for 1 hour, the particles disappear or the particle size (particle diameter) changes by 10% or more.

[0100] On the other hand, an epoxy resin-insoluble thermoplastic resin refers to a thermoplastic resin that is substantially insoluble in epoxy resin at or below the temperature at which a fiber-reinforced composite material is molded. That is, when 10 parts by mass of a thermoplastic resin having 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 10% or more. Generally, the temperature at which fiber-reinforced composite materials are molded is 100 to 190°C. The particle size is measured visually using a microscope, and the average particle size refers to the average particle size of 100 randomly selected particles.

[0101] If the epoxy resin-soluble thermoplastic resin is not completely dissolved, it dissolves in the epoxy resin when heated during the curing process of the epoxy resin, thereby increasing the viscosity of the matrix resin, thereby preventing the flow of the matrix resin (the phenomenon in which the matrix resin flows out of the reinforcing fiber substrate impregnated with the matrix resin) caused by a decrease in viscosity during the curing process.

[0102] The epoxy resin-soluble thermoplastic resin is preferably a resin that dissolves in the epoxy resin at 190°C in an amount of 80 mass % or more.

[0103] Specific examples of epoxy resin-soluble thermoplastic resins include polyethersulfone, polysulfone, polyetherimide, polycarbonate, etc. These may be used alone or in combination of two or more.

[0104] The content of the epoxy resin-soluble thermoplastic resin in the matrix resin is adjusted appropriately depending on the viscosity. From the viewpoint of processability of the prepreg and / or fiber-reinforced composite material, it 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 the epoxy resin contained in the matrix resin. If the content is less than 5 parts by mass, the impact resistance of the resulting fiber-reinforced composite material may be insufficient, which is not preferable. On the other hand, if the content of the epoxy resin-soluble thermoplastic resin exceeds 90 parts by mass, the viscosity will increase significantly, which may significantly deteriorate the handleability of the reinforcing fiber substrate impregnated with the matrix resin, which is not preferable.

[0105] The epoxy resin-soluble thermoplastic resin is preferably in the form of particles, which can be uniformly blended into the matrix resin, and the resulting prepreg and / or fiber-reinforced composite material has high moldability.

[0106] The average particle size of the epoxy resin-soluble thermoplastic resin is preferably 1 to 50 μm, more preferably 3 to 30 μm. If the particle size is less than 1 μm, the viscosity of the matrix resin will increase 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 the particle size 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 will be slow, resulting in a non-uniform fiber-reinforced composite material, which is also undesirable.

[0107] When the matrix resin contains a thermosetting resin, the matrix resin may contain an epoxy resin-insoluble thermoplastic resin in addition to the epoxy resin-soluble thermoplastic resin. Part of the epoxy resin-insoluble thermoplastic resin and the epoxy resin-soluble thermoplastic resin (the epoxy resin-soluble thermoplastic resin that remains undissolved in the cured matrix resin) become dispersed as particles in 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.

[0108] Examples of epoxy resin-insoluble thermoplastic resins include polyamide, polyacetal, polyphenylene oxide, polyphenylene sulfide, polyester, polyamideimide, polyimide, polyether ketone, polyether ether ketone, polyethylene naphthalate, polyether nitrile, and polybenzimidazole. Among these, polyamide, polyamideimide, and polyimide are preferred due to their high toughness and heat resistance. Polyamide and polyimide are particularly effective in improving the toughness of fiber-reinforced composite materials. These may be used alone or in combination of two or more. Copolymers of these may also be used.

[0109] In particular, the heat resistance of the resulting fiber-reinforced composite material can be particularly improved by using polyamides such as amorphous polyimide, nylon 6 (registered trademark) (a polyamide obtained by a ring-opening polycondensation reaction of caprolactam), nylon 11 (a polyamide obtained by a ring-opening polycondensation reaction of undecane lactam), nylon 12 (a polyamide obtained by a ring-opening polycondensation reaction of lauryllactam), nylon 1010 (a polyamide obtained by a copolymerization reaction of sebacic acid and 1,10-decanediamine), and amorphous nylon (also called transparent nylon, which does not crystallize the polymer or has an extremely slow crystallization rate).

[0110] The content of the epoxy resin-insoluble thermoplastic resin in the matrix resin that can be used in the present invention is adjusted appropriately depending on 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 the epoxy resin contained in the matrix resin. If the content 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 exceeds 50 parts by mass, the impregnation of the matrix resin and the drapeability of the reinforcing fiber substrate impregnated with the matrix resin may be reduced, which is undesirable.

[0111] The preferred average particle size and shape of the epoxy resin-insoluble thermoplastic resin are the same as those of the epoxy resin-soluble thermoplastic resin.

[0112] <Production of fiber-reinforced composite materials>

[0113] The method for producing the fiber-reinforced composite material is not particularly limited, and a prepreg in which a reinforcing fiber substrate is previously impregnated with a matrix resin may be molded, or the reinforcing fiber substrate and the matrix resin may be compounded simultaneously with molding by a resin transfer molding method (RTM method), a resin film infusion molding method (RFI method), etc. Preferably, the reinforcing fiber substrate of the present invention is used in a molding method by the RTM method or the RFI method.

[0114] The fiber-reinforced composite material according to the present disclosure can be preferably produced by a method including the following steps: (a) impregnating the reinforcing fiber substrate according to the present disclosure with a matrix resin (impregnation step); and (b) subjecting the reinforcing fiber substrate impregnated with the matrix resin to a heat-curing treatment to obtain a fiber-reinforced composite material (heat-curing step).

[0115] (Impregnation Step) In the impregnation step, the reinforcing fiber substrate according to the present disclosure is impregnated with a matrix resin.

[0116] In the impregnation step, for example, the reinforcing fiber substrate is impregnated with a liquid resin (i.e., for example, an uncured curable resin or a molten thermoplastic resin) and cured or solidified to obtain the resin. For more detailed conditions of the impregnation step, see, for example, the following description of the RTM method.

[0117] (Heat curing step) In the heat curing step, the reinforcing fiber substrate impregnated with the matrix resin is heat cured to obtain a fiber reinforced composite material. For more detailed conditions of the heat curing step, see, for example, the following description regarding the RTM method.

[0118] (RTM Method) From the viewpoint of efficiently obtaining fiber-reinforced composite materials of complex shapes, the fiber-reinforced composite material according to the present disclosure is preferably obtained by the RTM method (resin transfer molding method). The RTM method includes a step of impregnating a reinforcing fiber substrate placed in a mold with a liquid thermosetting resin before curing or a molten thermoplastic resin as a matrix resin, and a step of curing or solidifying the matrix resin to obtain the fiber-reinforced composite material.

[0119] In the present invention, the mold used in the RTM method may be a closed mold made of a rigid material, or an open mold made of a rigid material and a flexible film (bag). In the latter case, a reinforcing fiber substrate can be placed between the open mold made of a rigid material and the flexible film. Various existing materials can be used as rigid materials, such as metals such as steel and aluminum, fiber-reinforced plastics (FRP), wood, and gypsum. Materials used for the flexible film include polyamide, polyimide, polyester, fluororesin, and silicone resin.

[0120] In the RTM method, when a closed mold made of a rigid material is used, the mold is usually clamped under pressure and the matrix resin is injected under pressure. In this case, a suction port can be provided in addition to the injection port and connected to a vacuum pump for suction. It is also possible to inject the matrix resin using suction only at atmospheric pressure without using a special pressurizing means. This method is suitable for producing large components by providing multiple suction ports.

[0121] In the RTM method, when an open mold made of a rigid material and a flexible film are used, suction may be performed and the matrix resin may be injected at atmospheric pressure alone without using any special pressurizing means. To achieve good impregnation with injection at atmospheric pressure alone, 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.

[0122] When an epoxy resin is used as the matrix resin, the impregnation pressure when the epoxy resin is impregnated into a reinforcing fiber substrate by the RTM method is determined appropriately taking into consideration the viscosity and resin flow of the resin. Specific impregnation pressures are 0.001 to 10 MPa, and preferably 0.01 to 1 MPa. When a fiber-reinforced composite material is obtained 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.

[0123] 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-cured. The mold temperature during heat-curing is usually selected to be higher than the mold temperature during injection of the thermosetting resin. 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 fiber-reinforced composite material is removed from the mold. The resulting fiber-reinforced composite material may then be post-cured at a higher temperature. The post-curing temperature is preferably 150 to 200°C, and the post-curing time is preferably 1 minute to 4 hours.

[0124] The amount of the matrix resin is preferably 20 to 60 parts by mass, more preferably 30 to 40 parts by mass, per 100 parts by mass of the reinforcing fiber substrate.

[0125] In this molding method, the viscosity of the matrix resin at the injection temperature is preferably 0.01 to 1 Pa·s. It is preferable to adjust the viscosity at the time of injection to within the above range by treating the resin to be injected in advance by a method such as heating.

[0126] (Microcracks) The fiber-reinforced composite material according to the present disclosure has a reinforcing fiber substrate according to the present disclosure, and therefore has a reduced crack density. Specifically, the crack density after a thermal shock test is preferably less than 0.5 cracks / (cm ply), more preferably 0.4 cracks / (cm ply) or less, and even more preferably 0.3 cracks / (cm ply) or less.

[0127] The thermal shock test for measuring the crack density after the thermal shock test can be performed as follows: A thermal shock tester is used to apply 1,000 thermal cycles to the fiber-reinforced composite material. One thermal cycle is set to consist of a 15-minute plateau at 55°C, followed by a 15-minute temperature change region reaching a temperature of 70°C, followed by a 15-minute plateau at 70°C, followed by a 15-minute temperature change region returning to a temperature of -55°C, and this cycle is repeated 1,000 times.

[0128] The crack density after thermal shock test can be measured as follows: The number of cracks in the cross section inside the test piece of the fiber-reinforced resin composite material after the thermal shock test is counted by observation under a microscope at 200 times magnification. More specifically, the test piece (width 80 mm × length 50 mm × thickness 5 mm) after the thermal shock test is cut into four equal parts of width 40 mm × length 25 mm, the cut surface in the thickness direction is mirror-polished, and each of the long side and short side is used as an observation surface. The observation range of microcracks in the microscope observation is 50 mm. ２ The crack density value is calculated by dividing the number of cracks measured by the number of layers and the width of the observation surface. The unit of crack density is pieces / (cm ply). The crack density values ​​obtained by observing the long and short sides are averaged to obtain the final crack density.

[0129] <Applications> Applications of the reinforcing fiber substrates, preform materials, and fiber-reinforced composite materials (composites) according to the present disclosure include, for example, structural materials for aircraft, automobiles, railroad vehicles, and ships. In other words, the reinforcing fiber substrates according to the present disclosure and composites produced using the same can be used as materials for constructing bodies of aircraft, automobiles, railroad vehicles, ships, and the like.

[0130] The present invention will now be described in more detail with reference to the following examples, which do not limit the present invention.

[0131] <Evaluation Method> Evaluations in the examples and comparative examples were carried out as follows.

[0132] (Melting Point of Thermoplastic Resin) The melting point of the thermoplastic resin of the thermoplastic resin fiber constituting the nonwoven fabric as the resin material layer (veil layer) was measured in accordance with JIS K7121. Specifically, 3 mg of the nonwoven fabric was weighed into an aluminum pan and used as a sample. Using a DSC (DSC3500 Sirius manufactured by NETZSCH), the temperature at the peak of the melting endothermic peak was measured as the melting point of the nonwoven fabric. When there were multiple melting endothermic peaks, the value measured on the lowest temperature side was taken as the melting point of the nonwoven fabric. [Measurement Conditions] Measurement temperature range: room temperature to 250°C Heating rate: 5°C / min

[0133] (Average Fiber Diameter of Thermoplastic Resin Fibers) The average fiber diameter (μm) of the thermoplastic resin fibers constituting the nonwoven fabric as the resin material layer was measured by averaging the fiber diameter values ​​measured for at least 30 fibers using an optical microscope, VHX-5000 manufactured by Keyence Corporation, at 300x magnification.

[0134] (Molecular Weight of Thermoplastic Resin) The molecular weights (number average molecular weight Mn and weight average molecular weight Mw) of the thermoplastic resin constituting the thermoplastic resin fiber were each measured by the GPC method. Specifically, a nonwoven fabric sample was dissolved overnight in HFIP (hexafluoroisopropanol) to a concentration of 1 mg / mL, and the next day was filtered through a 0.5 μm membrane filter, and the filtrate was measured under the following conditions. Apparatus: HPLC-8320GPC EcoSEC manufactured by Tosoh Corporation Column: TSK-gel Super HM-M x 2 Mobile phase: HFIP containing 5 mM sodium trifluoroacetate Flow rate: 0.3 mL / min Column temperature: 40°C Injection volume: 20 μL Standard PMMA: EasiVial PM Measurement concentration: 1 mg / mL Detector: RI (Refractive Index Detector)

[0135] (Polydispersity of Thermoplastic Resin) The polydispersity Mw / Mn of the thermoplastic resin constituting the thermoplastic resin fiber was calculated from the number average molecular weight Mn and the weight average molecular weight Mw calculated by the GPC method.

[0136] (Thermal Shock Test) The fiber reinforced composite material was subjected to 1000 thermal cycles using a thermal shock tester (TSA-73EH-W manufactured by Espec Corp.). One thermal cycle consisted of a 15-minute plateau at −55° C., followed by a 15-minute temperature change period up to 70° C., followed by a 15-minute plateau at 70° C., followed by a 15-minute temperature change period back to −55° C., and this cycle was repeated 1000 times.

[0137] (Crack Density) The number of cracks on the cross section inside the fiber-reinforced composite material test piece after the thermal shock test was counted by microscopic observation. A VHX-5000 microscope manufactured by Keyence Corporation was used as the microscope, and observation was performed at 200x magnification. Specifically, the test piece after the thermal shock test (width 80 mm × length 50 mm × thickness 5 mm) was cut into four equal pieces of width 40 mm × length 25 mm, and the cut surfaces in the thickness direction were mirror-polished, with each of the long side and short side being used as the observation surface. The observation range for microcracks in the microscopic observation was 50 mm. ２ The crack density value is calculated by dividing the number of cracks measured by the number of layers (ply = number of 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 the observation of the long side and short side were averaged to obtain the final crack density.

[0138] The evaluation criteria for "microcrack resistance" in Table 1 below are as follows: "Good": The crack density was less than 0.5 cracks / (cm ply). "Poor": The crack density was 0.5 cracks / (cm ply) or more.

[0139] (Compression strength after impact (CAI)) The carbon fiber reinforced resin composite material was cut to a size of 101.6 mm wide x 152.4 mm long to obtain a test specimen for compression after impact (CAI) testing. Using this test specimen, an impact of 30.5 J was applied to damage the specimen in accordance with SACMA SRM 2R-94, and then the compressive strength after impact CAI (unit: MPa) was measured. The crosshead speed of the test specimen compression tester was 1 mm / min, and five test specimens were measured.

[0140] (Molding Robustness) The molding robustness of carbon fiber reinforced plastic composites (CFRP) was evaluated based on the difference in panel thickness when CFRP was molded using matrix resins with different curing times. Specifically, the thicknesses of CFRP molded using matrix resin M-1 (curing conditions: 180°C, 120 minutes) described below and CFRP molded using matrix resin M-2 (curing conditions: 180°C, 30 minutes) described below were measured, and the molding robustness of the CFRP was evaluated based on the absolute value of the difference between the thicknesses (absolute value of the thickness difference). The CFRP panel thickness was measured using a micrometer.

[0141] The evaluation criteria for molding robustness in Table 1 below are as follows: "Good": The absolute value of the difference in thickness was less than 0.20 mm. "Poor": The absolute value of the difference in thickness was 0.20 mm or more.

[0142] (MVR) The MVR (melt volume rate) of the thermoplastic resin fiber constituting the nonwoven fabric as the resin material layer was measured with reference to JIS K7210-1 Method B. The measurement conditions were as follows: Apparatus: MELT INDEXER G-02 (manufactured by Toyo Seiki Seisakusho, Ltd.) Test temperature: 275°C Nominal load: 2.16 kg

[0143] <Constituent Elements> The materials used in the examples and comparative examples are described below.

[0144] (Reinforcing fiber) The following carbon fiber bundles were used as reinforcing fibers: Carbon fiber bundle "Tenax (registered trademark)" (manufactured by Teijin Limited, product number: HTS45-12K, tensile strength 4.5 GPa, tensile modulus 240 GPa, linear expansion coefficient -0.5 × 10-6 / K) (Unidirectional woven fabric (UD)) Unidirectional woven fabric S-1: Dry Reinforcements Woven Fabric DRWF HTS45-UD manufactured by TEIJIN CARBON EUROPE GmbH, reinforcing fiber HTS45-12K, reinforcing fiber basis weight 194 g / m ２ This reinforcing fiber substrate (unidirectional woven fabric S-1) is a woven fabric composed of the above-mentioned carbon fiber bundles HTS45-12K as reinforcing fibers aligned in one direction as warp yarns, and the following auxiliary yarns as weft yarns, and is a so-called rattan woven fabric. - Weft direction auxiliary yarn (weft yarn): Grilon (registered trademark) K-85 manufactured by EMS-CHEMIE AG, a composite fiber of polyamide resin and polyester resin, fineness 200 dtex, number of single yarns 44, melting point 86 ° C (auxiliary yarn as stitch yarn) As the stitch yarn as auxiliary yarn, stitch yarn A-1 (JOINER (registered trademark) H-Type manufactured by Fujibo Holdings Inc., copolymer polyamide resin fiber, fineness 33 dtex, number of single yarns 5, melting point 131 ° C) was used.

[0145] (Matrix Resin) A liquid thermosetting epoxy resin was used as the matrix resin for the carbon fiber reinforced resin composite material (composite). The compositions (M-1 and M-2) are as follows:

[0146] Matrix resin M-1 (curing conditions: 180°C, 120 minutes): (epoxy resin) Tetraglycidyl-4,4'-diaminodiphenylmethane (Araldite (registered trademark) 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 (MX-414 (product name) manufactured by Kaneka Corporation, average particle diameter 0.11 μm, masterbatch obtained by dispersing a particulate polybutadiene rubber component in a glycidylamine-type tetrafunctional epoxy resin to a concentration of 25% by mass) 19 parts by mass (curing agent) 4,4'-diamino-3,3'-diisopropyl-5,5'-dimethyldiphenylmethane (Lonzacure (registered trademark) M-MIPA d manufactured by Arcsada Japan Co., Ltd.) 31 parts by mass Diethyltoluenediamine (Lonzacure (registered trademark) DETDA80, manufactured by Arcsada Japan Co., Ltd.) 21 parts by mass

[0147] Matrix resin M-2 (curing conditions: 180°C, 30 minutes): (epoxy resin) Tetraglycidyl-4,4'-diaminodiphenylmethane (Araldite (registered trademark) MY721 manufactured by Huntsman Japan Co., Ltd.) 17.5 parts by mass N,N-diglycidylaniline (GAN (product name) manufactured by Nippon Kayaku Co., Ltd.) 11.4 parts by mass (resin particle component) MX-414 (MX-414 (product name) manufactured by Kaneka Corporation, average particle diameter 0.11 μm, masterbatch obtained by dispersing a particulate polybutadiene rubber component in a glycidylamine-type tetrafunctional epoxy resin to a concentration of 25% by mass) 12.1 parts by mass (curing agent) 4,4'-diamino-3,3'-diisopropyl-5,5'-dimethyldiphenylmethane (Arcsada Japan Co., Ltd.) Lonzacure (registered trademark) M-MIPA d) 9.8 parts by mass Diethyltoluenediamine (Lonzacure (registered trademark) DETDA80 manufactured by Arcsada Japan Co., Ltd.) 8.8 parts by mass 4-methoxybenzylamine (4MxBA manufactured by Tokyo Chemical Industry Co., Ltd.) 1.0 part by mass

[0148] (Raw Materials for Resin Material Layer) The following thermoplastic resins were used for the thermoplastic resin fibers that make up the resin material layer. Polyamide 11 (PA11, melting point 184-187°C, manufactured by ARKEMA Co., Ltd., product name Rilsan) Polyamide 612 (PA612, melting point 216°C, manufactured by Daicel-Evonik Co., Ltd., product name VESTAMID DX9308) Polyamide 6 / Polyamide 12 copolymer (PA6 / PA12 copolymer, melting point 197°C, manufactured by EMS-CHEMIE, product name Grilon K-203) Polyamide 12 (PA12, melting point 177°C, manufactured by Daicel-Evonik Co., Ltd., product name DAIAMID L1640) Polyamide 1010 (PA12, melting point 199°C, manufactured by Daicel-Evonik Co., Ltd., product name VESTAMID TERRA DS16) Polyamide 610 (PA610, melting point 222°C, manufactured by Daicel-Evonik Ltd., product name TeRRA DS16) Polyamide 66 (PA66, melting point 268°C)

[0149] (Resin Material Layer) The following nonwoven fabrics were used as the resin material layer, which were produced by a melt-blowing method using the above resin raw materials: Nonwoven fabric B-1: Polyamide PA11, average fiber diameter 6.1 μm, basis weight 5 g / m ２ Nonwoven fabric B-2: Polyamide PA612, average fiber diameter 6.6 μm, basis weight 5 g / m ２ Nonwoven fabric B-3: Polyamide PA12, average fiber diameter 7.7 μm, basis weight 5 g / m ２ Nonwoven fabric B-4: Polyamide PA1010, average fiber diameter 7.7 μm, basis weight 5 g / m ２ Nonwoven fabric B-5: Polyamide PA610, average fiber diameter 7.6 μm, basis weight 5 g / m ２ Nonwoven fabric B-6: Polyamide PA66, average fiber diameter 6.3 μm, basis weight 5 g / m ２

[0150] The resin material layer was made of the following nonwoven fabric manufactured by a spunbond method: Nonwoven fabric B-7: Polyamide PA11, average fiber diameter 38.0 μm, basis weight 6 g / m ２ Nonwoven fabric B-8: Polyamide PA6 / PA12 copolymer, average fiber diameter 42.9 μm, basis weight 4 g / m ２Nonwoven fabric B-9: Polyamide PA12, average fiber diameter 49.5 μm, basis weight 6 g / m ２

[0151] Examples 1 to 5 and Comparative Examples 1 to 6 Reinforcing fiber substrates according to Examples 1 to 5 and Comparative Examples 1 to 6 were prepared, and carbon fiber reinforced composite materials (CFRP) were produced from these reinforcing substrates, and their physical properties were evaluated.

[0152] In Examples 1 to 3 and Comparative Examples 1 to 6, reinforcing fiber substrates having non-crimp fabric (NCF) were produced.

[0153] Example 1 (Production of a reinforcing fiber substrate having a non-crimp fabric (NCF)) Four reinforcing fiber sheets were prepared by unidirectionally aligning 200 of the reinforcing fibers (carbon fiber bundles), and these reinforcing fiber sheets were stacked at angles of -45°, 0°, +45°, and 90° in that order. Furthermore, the nonwoven fabric B-1 was placed between each layer of the reinforcing fiber sheets. In this way, a laminated sheet was prepared in which four reinforcing fiber sheets with fibers unidirectionally aligned and nonwoven fabrics were placed between them.

[0154] Next, the laminated sheet was sewn (stitched) through the thickness direction with the above stitch thread A-1 as an auxiliary thread to form the reinforcing fiber substrate according to Example 1 (reinforcing fiber basis weight per layer: 190 g / m ２ , Stitch thread usage: 4g / m ２ , Total basis weight of reinforcing fiber substrate: 760 g / m ２ ) was obtained.

[0155] (Production of carbon fiber reinforced resin composite material) Next, a carbon fiber reinforced composite material was produced by resin transfer molding (RTM) using the obtained reinforcing fiber substrate and liquid thermosetting resin. First, on the substrate, a peel cloth Release Ply C (manufactured by AIRTECH) which is a substrate imparted with a release function and a resin diffusion substrate Resin Flow 90HT (manufactured by AIRTECH) were laminated. Then, hoses for forming a resin inlet and a resin outlet were arranged, the whole 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., and the pressure inside the bag was reduced to 5 Torr or less, and then a liquid thermosetting resin (matrix resin M-1) heated to 100 ° C. was injected into the vacuum system through the resin inlet (35 parts by mass per 100 parts by mass of the substrate). The bag was filled with the injected liquid thermosetting resin, and the temperature was raised to 180°C while the substrate was impregnated with the resin. The resin was then held at 180°C for 120 minutes to cure the resin, thereby obtaining a carbon fiber reinforced composite material (CFRP).

[0156] When matrix resin M-2 was used as the liquid thermosetting resin, the liquid thermosetting resin was injected in the same manner as above, and the temperature was raised to 180°C. After that, the thermosetting resin was cured by holding the temperature at 180°C for 30 minutes, thereby obtaining a carbon fiber reinforced composite material (CFRP).

[0157] The resulting carbon fiber reinforced composite materials (using matrix resin M-1) were measured for CAI (compressive strength after impact) and crack density. Furthermore, the molding robustness was evaluated as described above for the carbon fiber reinforced composite materials using M-1 and M-2 as matrix resins. The results are shown in Table 1 below.

[0158] Example 2 A reinforcing fiber substrate and a carbon fiber reinforced composite material according to Example 2 were produced and evaluated in the same manner as in Example 1, except that the thermoplastic resin fibers constituting the resin material layer had the properties shown in the following Table 1. The evaluation results are shown in the following Table 1.

[0159] Example 3 A reinforcing fiber substrate and a carbon fiber reinforced composite material according to Example 3 were produced and evaluated in the same manner as in Example 1, except that the thermoplastic resin fibers constituting the resin material layer had the properties shown in the following Table 1. The evaluation results are shown in the following Table 1.

[0160] <Examples 4 and 5> In Examples 4 and 5, reinforcing fiber substrates having a unidirectional woven fabric (UD) were produced. (Production of reinforcing fiber substrate) The nonwoven fabric B-1 or nonwoven fabric B-7 was placed on the surface of the unidirectional woven fabric S-1 to produce the reinforcing fiber substrates of Examples 4 and 5, respectively. Except for using the reinforcing fiber substrates obtained in this manner, the reinforcing fiber substrates and carbon fiber reinforced composite materials of Examples 4 and 5 were produced and evaluated in the same manner as in Example 1, and the evaluation results are shown in Table 1 below.

[0161] <Comparative Examples 1 to 6> Reinforced fiber substrates and carbon fiber reinforced composite materials according to Comparative Examples 1 to 6 were produced and evaluated in the same manner as in Example 1, except that the thermoplastic resin fibers constituting the resin material layer had the properties shown in the following Table 1. The evaluation results are shown in the following Table 1.

[0162]

[0163] In Examples 1 to 5, the melting point of the thermoplastic resin fiber constituting the resin material layer (veil layer) was 184°C to 216°C and the molecular weight Mw was 18,900 to 24,000, and good microcrack resistance, mechanical strength (CAI), and molding robustness were confirmed.

[0164] In contrast, in Comparative Examples 1, 4, and 5, the melting point of the resin in the thermoplastic resin fiber was relatively high, 197 to 222°C, so the molding robustness was good, but the molecular weight Mw was high, 32,700 to 33,200, so the microcrack resistance was poor. Comparative Example 1 showed a relatively low CAI value, while Comparative Examples 4 and 5 showed relatively high CAI values.

[0165] In Comparative Examples 2 and 3, the melting point of the resin of the resin fiber constituting the veil layer was low at 177°C, and therefore, although the CAI (compressive strength after impact) and microcrack resistance were good, the molding robustness was poor.

[0166] In Comparative Example 6, the melting point of the thermoplastic resin fiber constituting the veil layer was excessively high at 268°C, and therefore, although the molding robustness was good, the CAI (compressive strength after impact) and microcrack resistance were poor. When the melting point of the thermoplastic resin fiber resin is excessively high, even if the molecular weight is relatively low, the entanglement of the molecular chains of the resin constituting the veil layer is difficult to loosen when subjected to heat treatment during curing, which is thought to reduce the affinity (adhesion) between the thermoplastic resin fiber constituting the veil layer and the matrix resin, resulting in the occurrence of microcracks.

[0167] 10, 30 Reinforced fiber substrate 40 Non-crimp fabric 22, 42 Reinforced fiber 24, 44 Auxiliary yarn L direction 110, 310, 312, 314, 316 Resin material layer 130, 330, 340, 350 Reinforced fiber layer

Claims

1. A reinforcing fiber substrate having one or more reinforcing fiber layers containing reinforcing fibers, and one or more resin material layers containing thermoplastic resin fibers, wherein the melting point of the thermoplastic resin is greater than 180°C and less than 250°C, and the weight average molecular weight Mw of the thermoplastic resin is 15,000 to 28,000.

2. The reinforcing fiber substrate according to claim 1, wherein the polydispersity (Mw / Mn) of the thermoplastic resin is 1.40 to 1.

80.

3. The reinforcing fiber substrate according to claim 1 or 2, wherein the thermoplastic resin is a polyamide resin or a polyester resin.

4. The reinforcing fiber substrate according to claim 1 or 2, wherein the thermoplastic resin is a polyamide resin.

5. The reinforcing fiber substrate according to claim 1 or 2, wherein the average fiber diameter of the thermoplastic resin fibers is 1 μm to 60 μm.

6. The reinforcing fiber substrate according to claim 1 or 2, wherein the one or more resin material layers are made of a nonwoven fabric containing thermoplastic resin fibers.

7. The reinforcing fiber substrate according to claim 6, wherein the one or more resin material layers are made of a long-fiber nonwoven fabric containing thermoplastic resin fibers.

8. A reinforced fiber substrate according to claim 1 or 2, wherein the one or each of the plurality of resin material layers is disposed on a surface of the one or each of the plurality of reinforcing fiber layers.

9. The reinforcing fiber substrate according to claim 1 or 2, wherein the reinforcing fiber layer is a unidirectional woven fabric having the reinforcing fibers aligned in one direction as warp threads and auxiliary threads as weft threads.

10. The reinforcing fiber substrate according to claim 1 or 2, wherein the reinforcing fiber substrate includes at least two reinforcing fiber layers that are stacked on top of each other, the at least two reinforcing fiber layers are each composed of reinforcing fibers aligned in one direction, and the at least two reinforcing fiber layers are sewn together by a stitch thread as an auxiliary thread.

11. The reinforcing fiber substrate according to claim 1 or 2, wherein the reinforcing fiber is a carbon fiber.

12. A preform material comprising the reinforcing fiber substrate according to claim 1 or 2 and a binder resin.

13. A method for producing a preform material, comprising heating under pressure a composite containing the reinforcing fiber substrate according to claim 1 or 2 and a binder resin.

14. A fiber-reinforced composite material comprising the reinforcing fiber substrate according to claim 1 or 2, and a matrix resin impregnated into the reinforcing fiber substrate.

15. A method for producing a fiber-reinforced composite material, comprising: impregnating the reinforcing fiber substrate according to claim 1 or 2 with a matrix resin; and subjecting the reinforcing fiber substrate impregnated with the matrix resin to a heat curing treatment to obtain a fiber-reinforced composite material.

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